HISTORICALLY “ballistics” has been the study of the behavior of a projectile—a ball, bullet, arrow, dart, quarrel, artillery shell, or pie—anything that makes its way through the air from one place to another powered by an initial impetus. The word derives from the name of a weapon used by the ancient Romans, the ballista, an oversized windup crossbow they used to hurl heavy darts or even heavier stones at their enemies. The term is still used within the shooting community to denote the study of the effects of gravity and wind resistance on a projectile of a given shape, mass, and velocity, fired at a given angle.
Over the past eighty years or so the forensic definition of ballistics has expanded to include everything having to do with projectile weapons and the objects shot from them. Forensic ballistics is concerned with the characteristics of a weapon, the nature of its explosive charge, the shape and composition of the projectile, the effects of the projectile’s progress through the barrel of the weapon, and the means of identifying the particular weapon from which the projectile was fired.
If a projectile weapon is used to commit a crime, there will be questions for the ballistics expert: Just what sort of weapon is this? Who made it, and how might it have gotten here? What sort of projectile does it fire? Is this the actual weapon from which the projectile was fired? From what distance was it fired? Is this ammunition consistent with the ammunition found at the suspect’s house? Was the shooting accidental or deliberate?
Until the early years of the twentieth century, the police consulted a gunsmith when they needed information about a gun. But many of the questions of interest to criminal investigators are outside the experience of the average gunsmith. As Hans Gross explained in 1906:
Even when dealing with a gunsmith who knows his trade, we find his knowledge restricted in most cases to being able to indicate the origin and the price of the weapon, the names of its different parts, and other mechanical details, which it must be confessed, will have in most cases a certain value. But he will not be able to say much regarding the use to which the instrument may be put, the effects which it is capable of producing, the connection existing between the arm itself and the bullet employed, besides numerous other questions of capital importance.
Gross suggested that the criminal investigator with a firearms question might have to turn to experts in other fields—“the experienced sportsman, the medical man, the inspector of musketry, the physicist, the chemist and the microscopist.”
In order to encompass this breadth of expertise in one person, another fund of knowledge had to be built up, knowledge of great interest to the police but with little application elsewhere. It wasn’t until the 1930s that crime labs could identify and train people who could honestly call themselves ballistics experts.
The first known apprehension of a murderer through what we now call ballistics evidence occurred in England in 1794. The victim was Edward Culshaw of Lancashire, and the suspect was John Toms. The weapon was a muzzle-loading flintlock pistol.
To load a muzzle-loader one first poured a measured amount of gunpowder into the barrel, then rammed in a wad of paper. Next, one dropped in the ball, then rammed down another wad of paper to jam the ball in so it would not simply roll out. Then one put a dash of gunpowder in the pan, which connected to the gunpowder in the barrel through a thin tube bored through the side. To fire the thing, one cocked a hammer holding a flint and pulled the trigger. As the flint hit the pan, a spark ignited the exterior gunpowder and a flame raced through the tube and ignited the interior gunpowder. The powder burned rapidly, creating a large volume of hot gas that blew the ball down the barrel and out.
Usually. Sometimes the spark did not successfully ignite the exterior gunpowder. Sometimes the powder just flashed up without sending the flame down the tube (hence the expression “a flash in the pan”).
Back to Mr. Toms, who was suspected of shooting Mr. Culshaw. The pistol had in fact fired, and the ball had raced through the air and lodged in Mr. Culshaw’s skull. With it had gone the paper wad that had held the ball in place. The surgeon who removed the ball from the victim’s skull also found the paper wad intact and carefully unfolded it. When Toms, who was for other reasons the logical suspect, was arrested and searched, he had a handbill in his pocket. The missing corner of this handbill exactly matched the wad removed from the victim. Mr. Toms went to the gallows.
In 1835 Henry Goddard, then a member of the Bow Street Runners, the precursor organization to the London Police (and later the chief constable of Northamptonshire), noticed that a bullet removed from a murder victim had a small pimple on one side. When he searched a suspect’s home he found a bullet mold with a defect in it that would cause bullets cast from it to carry a small pimple on one side. He pointed this out to the suspect, who promptly confessed.
In August 1876 a British police constable named Cock was murdered in Whalley Range, Manchester. Two brothers named Habron were tried for the murder. One was acquitted, but the other, William, was convicted and sentenced to death. His sentence was commuted to “penal servitude for life” a few weeks later, however, as it was felt that he must have had an accomplice (someone other than his brother), and that the accomplice had fired the fatal shot. The day after the Habron trial ended, a man named Arthur Dyson was murdered in Ecclesall, a suburb of Sheffield. The killer was seen and recognized as Charles Peace, an habitual criminal. Peace wasn’t caught until two years later when he shot and wounded a police constable named Robinson while attempting a burglary at Blackheath. On his way to the gallows for the Dyson murder, Peace confessed to the murderer of Constable Cock and declared that he had acted alone.
The police didn’t want to believe him, but they nevertheless compared the bullets from PC Robinson, Arthur Dyson, and PC Cock. All had been fired from the same—Peace’s—gun. The means they used to compare the bullets isn’t revealed, but this is one of the earliest known examples of a true ballistics examination. William Habron was released from prison and compensated for the inconvenience of having three years of his life taken from him.
Because of the ubiquitousness of handguns in the United States, and because of the common confusion of propinquity for knowledge, many Americans consider themselves to be firearms experts. Most of them are mistaken. Fifty years ago some of these same misguided people set themselves up as ballistics experts and testified in criminal trials, to the detriment of justice in many cases. In the introduction to his landmark 1935 book, Firearms Investigation, Identification and Evidence, J. S. Hatcher observes:
In cases of death by shooting, it frequently happens that the life or liberty of a suspected person may depend entirely upon the ability of the authorities to determine what kind of weapon did the shooting, or whether a fired cartridge or bullet involved in the fatality did or did not come from a certain gun. The knowledge of firearms and explosives and how they act that is possessed by the public at large, including most peace officers and members of the legal profession, is so meager that almost unbelievable mistakes in testimony vitally affecting the guilt or innocence of an accused person are continually occurring.
During the past twenty or more years, the author has had occasion to observe many instances in which the apprehension of some individual responsible for a crime with firearms or explosives has been delayed or rendered impossible by lack of even a small amount of knowledge of the right kind by the detectives or police who made the investigation. He has observed other instances in which attorneys, courts and juries have been imposed on or misled by insufficiently informed or unscrupulous individuals who have managed to qualify as expert witnesses on firearms.
A spinning top tends to point in the same direction, and, if it is spinning fast enough, it strongly resists any attempt to change its direction. A rapidly spinning gyroscope is so change resistant that it may be used as a compass. Similarly, a football will fly straight and true if the passer imparts a spin to it as he throws. Absent the spin, a football will tumble, yaw, and end up anywhere. Likewise, if you put a point on a bullet and impart a spin to it as it’s fired, it has a much better chance of going where it’s aimed.
In the eighteenth century, to give the bullet a spin and encourage it to fly straight, gun makers got the idea of cutting spiraling grooves into a gun barrel. These grooves and “lands”—the surfaces left between the grooves—were together called rifling. The guns that featured rifling became known as rifles. During the American Revolution the Kentucky rifles made by German gunsmiths in Pennsylvania and carried by the frontiersmen were accurate to a far greater distance than the smoothbore muskets used by British troops. George Hanger, a colonel in the British army, became interested in this phenomenon when his bugler’s horse was shot out from under him at a distance that Hanger measured several times—a “full 400 yards.”
“I have many times asked the American backwoodsman what was the most their best marksmen could do,” he reported. “They have constantly told me that an expert marksman, provided he can draw good & true sight, can hit the head of a man at 200 yards.” The British army’s standard-issue musket, nicknamed “Brown Bess,” even under the best conditions was barely accurate at 50 yards.
But a rifle must also have a close fit between bullet and barrel. Otherwise the gases simply blow out through the grooves. And it was difficult to ram a tight-fitting bullet down a muzzle-loading rifle. With the perfection of the breech-loader in the mid-nineteenth century, the musket slowly faded away as breech-loading rifles and rifled handguns came into wide use. The number of rifling grooves in these new guns usually varied from four to seven. The direction of the twist—either right- or left-handed—depended on the whim of the maker.
In 1899 Alexandre Lacassagne, a professor of forensic medicine at the University of Lyons, became the first known person to compare markings on a bullet taken from the body of a murder victim to the rifling found in the handguns belonging to several suspects. He found that the bullet had seven longitudinal grooves created by its passage through a rifled barrel. Only one of the weapons he examined had seven matching grooves. The owner of this gun was duly convicted of murder.
CONDEMNED MEN ARE FREED BY A PARDON
Auburn, N.Y., May 9.—Charles F. Stielow, who was pardoned by Governor Whitman after serving three years of a life sentence following his conviction on the charge of murdering Charles B. Phelps and his housekeeper, Margaret Wolcott, at West Shelby, in March 1915, was released from Auburn prison today. He left at once for Buffalo. Nelson Green, who was sentenced to twenty years as an accessory of Stielow and who also was pardoned by the governor, was released at the same time.
—Altoona Tribune, May 10, 1918
The scientific investigation of ballistics evidence in the United States could be said to have begun during and because of the 1915 case of Charlie Stielow and Nelson Green. Early on the morning of March 22 Stielow, described as “an illiterate, good-natured tenant farmer,” left his house in Orleans County, New York, to discover a dead woman in a nightgown on his doorstep. Footsteps in the fresh snow showed that she had come from the nearby house of Charles B. Phelps, Stielow’s boss and the owner of the farm. When Stielow bent over to take a close look at the woman, he recognized Margaret Wolcott, Phelps’s housekeeper. She had been shot in the chest (right through the heart, as it turned out). Hurrying over to the Phelps house, he found the kitchen door open and the ninety-year-old Phelps lying on the floor. He had three bullet holes in him and was barely alive. Stielow immediately ran to a neighbor’s house and gave the alarm.
The local police, unaccustomed to serious investigation, came to the Phelps house and wandered about, accomplishing nothing constructive and managing to tramp over any forensic evidence that might have been present. The Orleans County authorities hired George W. Newton, a private detective from Buffalo, New York, to investigate. Ten days later, at Newton’s suggestion, the police arrested Nelson Green, Stielow’s brother-in-law, who lived with Phelps and Phelps’s wife. They took him down to the station house where by two o’clock the next morning Newton had him signing a confession that went into great detail about how he and Stielow had committed the murders. When Stielow was arrested, he duly confessed.
The two men told roughly the same story. Considering that they had been held separately and that they had not actually committed the crime, this says something about the persuasiveness of Detective Newton’s interrogation techniques. According to their confessions, they had knocked on the kitchen door. When Phelps came to answer, they shot him and then headed for his bedroom, where they thought he kept his money. Just then Margaret Wolcott came running out of her room and through the kitchen door, slamming the door behind her. Either Green or Stielow (each man claimed the other had done all the shooting) had then fired at the housekeeper through the glass panel in the kitchen door before returning to the bedroom and searching for the money. Each suspect confessed that the two had found about two hundred dollars and that the other man had kept it.
When they returned to their own house, they found a wounded Margaret Wolcott pounding at the front door and screaming to be let in. So they entered at the back of the house and allowed her to scream until she died.
Newton discovered that they had lied when they both denied owning a weapon. Stielow had given both a .22 caliber revolver and a .22 rifle to a relative to hide. The victims had been killed with a .22.
Stielow was tried first and, though he repudiated his confession, saying that it had been coerced, it was admitted into evidence. All that remained was to tie the bullets recovered from the victims’ bodies to one of Stielow’s guns. The prosecution relied on Dr. Albert Hamilton, a self-styled firearms expert from Auburn, New York. A patent-medicine hawker who had awarded himself a medical degree, Hamilton had recently become an expert in all things forensic. In addition to firearms, he would render his learned opinion on matters chemical, toxicological, microscopical, and anatomical. He would expertly analyze bloodstains and handwriting as well as conduct autopsies.
“Doctor” Hamilton testified that he had microscopically examined Stielow’s revolver and found nine defects at the end of the muzzle that matched nine scratches in each of the four bullets taken from the bodies. When asked why these scratches didn’t show up on enlarged photographs of the bullets, he replied that by some mistake, they were of the opposite end of the bullet.
Why, he was asked, would defects at the very end of the barrel mark the bullets? He replied:
The cylinder fitted so tightly against the rear of the barrel that there was no leakage of gas at the breech. The full force of the gas following the bullet out at the muzzle, the lead expands as it leaves the muzzle, fills in any depressions existing at the outer edge of the bore and receives scratches from the elevations existing between said depressions.
The jury, found Stielow guilty of murder in the first degree, and the judge sentenced him to death in the electric chair. Green pled guilty in order to escape electrocution, and was sentenced to life in prison.
In February 1916 an appeals court upheld the convictions, finding that, “from an examination of the record, it is inconceivable that the jury could have rendered any other verdict.”
While awaiting execution at Sing Sing, Stielow somehow managed to convince Deputy Warden Spencer Miller, Jr., that he might be innocent, or at least that his claims warranted attention. Miller told Louis Seibold, a reporter for the New York World, about the case. Seibold in turn hired a Buffalo detective named Thomas O’Grady to investigate. O’Grady discovered that both Stielow and Green were illiterate and that neither was capable of writing his confession or of employing some of the phrases that appeared in the documents. He also discovered that both Newton and Hamilton had worked on a contingency basis: they would not be paid unless Stielow and Green were found guilty.
In the meantime, second and third appeals for a new trial were denied. But the governor had taken an interest in the case, and on December 4, 1916, he commuted Stielow’s sentence to life in prison and appointed a Syracuse attorney named George Bond to look into it. Bond drafted Charles Waite, an investigator from the New York attorney general’s office, to assist him.
They quickly realized that the confessions of the two men did not correspond with the facts of the case. Both confessions had Margaret Wolcott running right past her two killers on her way out the door. If so, she must have recognized them. Yet she ran up to Stielow’s front door to ask for help. And, despite her having been shot through the heart, the men’s confessions had her still alive when they emerged from Phelps’s bedroom and returned to their house. In their confessions she cries, “Charlie, please let me in, I am dying!” In addition, the alleged angle of the bullet that hit Wolcott as she ran toward Stielow’s house was geometrically impossible. Anyone who bothered to visit the scene would have recognized this immediately.
Stielow’s .22 revolver was given to experts from the New York Detective Bureau. They examined it before test-firing it in order to judge how long it had been sitting without being fired. “Certainly three or four years, apparently a longer time,” was their conclusion. Then they wrapped a sheet of paper around it and fired one bullet. Instead of there being no leakage of gas at the breech as Dr. Hamilton had testified, the paper burst into flames from the heat and power of the discharged gases. Next, bullets were fired into a cotton-filled box and then taken to Dr. Max Poser, an expert in microscopic examination at the Bausch & Lomb headquarters in Rochester. Not only was he unable to find the microscopic scratches that Hamilton had sworn to, but he found that the murder bullets had been fired from a gun with a manufacturing flaw—it lacked one of the five grooves that were supposed to be in the barrel. Stielow’s gun could not have fired the bullets that killed Mr. Phelps and his housekeeper. Stielow and Green were promptly pardoned by the governor.
As a result of the Stielow case, Charles Waite realized that the ability to connect a bullet from a crime scene with a specific gun would be of great help in almost every case in which a bullet was collected from a crime scene. And a great step in that direction would be to assemble data on all the guns being manufactured: their bore diameters, the number and width of their lands and grooves, the pitch and direction of their rifling, and anything else that might leave a distinguishing mark on a bullet fired from them. For several years Waite traveled the country collecting data on firearms, poring through old record books, and interviewing the retired foremen of defunct arms companies, many of whom still kept their work notebooks.
At the end of World War I, when a flood of cheaply made foreign pistols came into the country, Waite found it necessary to spend time abroad, mostly in Europe, in order to broaden his information base.
Meanwhile in the 1920s, ballistics investigators Calvin Goddard and Philip Gravelle invented the comparison microscope, a binocular device in which each eyepiece looks through a separate microscope at a different viewing area. An earlier, simpler version was already in use for comparing grains or ground pigments. Goddard and Gravelle modified it so that bullets or shells could be compared simultaneously, side by side.
An early comparison microscope. The device was invented in the 1920s by Calvin Goddard and Philip Gravelle.
In 1925 Goddard and Gravelle teamed with Waite to establish the Bureau of Forensic Ballistics in New York City, from which they offered their combined expertise to law enforcement agencies around the country. In addition to weapons comparisons, the bureau offered fingerprinting, blood typing, and trace evidence analysis.
On St. Valentine’s Day 1929, two men dressed as policemen lined six hoodlums and a passing doctor against the wall of a garage at 2122 North Clark Street in Chicago. Two other men, wearing trench coats and carrying Thompson submachine guns (“Tommy” guns), entered the garage and fired seventy rounds at the lined-up men. Most of them died instantly, and none survived for more than a few hours. The shooters were escorted out by the “policemen” and disappeared. One survivor, a gangster named Frank Gusenberg, when asked who had shot him, managed to gasp, “I’m not gonna talk—nobody shot me.” He died on the garage floor with seventeen bullets in him. Hoodlum boss George “Bugs” Moran, the probable target of the killers, arrived too late to be included among the victims. When asked who he thought had done it, he replied, “Only Capone kills like that.”
About a year after the massacre, two Thompson submachine guns were found in the home of a known killer named Fred Burke as he was being arrested for the murder of a Michigan policeman. Goddard compared the St. Valentine’s Day murder bullets with test bullets fired through these Thompsons and identified the two guns as the murder weapons. Who actually used them in the garage that day is still a matter of speculation.
Over the years firearms examiners have expanded on and refined their techniques so that they can now exploit the many peculiarities of different weapons and their ammunition. The caliber of the bullet, the number and size of the rifling grooves in the barrel, and the position of the marks on the shell are known as “class characteristics.” All similar weapons will have the same characteristics. The barrels of all .45 caliber Colt automatic pistols, for instance, will have six rifling grooves with a left-hand twist. The groove depth in the Colt .45 is .003 5 inch, and the rate of twist is one full turn in 16 inches.
“Caliber” is the measure of the diameter of the bore (the hole the bullet goes through) in hundredths of an inch—a .30 caliber gun has a bore of 30 one-hundredths of an inch. But the simplicity of the system has become lost over time, and drift occurs. Thus the .38 caliber Colt special has a bore of only .346. And the so-called .38–40 has a bore of .401. And over the years many small-arms manufacturers have made specialty guns of unusual calibers.
The caliber of European guns is measured in millimeters; .30 caliber is, to the Europeans, 7.63 mm. The popular 9 mm caliber is .354 inch and therefore roughly corresponds to our standard .38 caliber, which, because of drift, is actually .359.
If you are examining a bullet under a microscope and you need to determine the rate of twist of the barrel, you must measure the diameter of the bullet and the angle the groove makes relative to a straight line drawn from the point of the bullet to the back. Then you get to use your high school geometry. The formula for determining the twist in inches is P = π × D ÷ tan a. P is pitch, D is the diameter of the bullet, and tan a is the tangent of the angle of the groove. For example, suppose you’re looking at a .45 caliber bullet with a diameter of .451 inch and you find the angle of the groove to be 5° 04'. Your scientific calculator tells you that the tangent of 5° 04' is .0885. You multiply pi (3.14159) times the diameter and get 1.4168. Divide that by .0885 and you discover that the twist is one turn in 16 inches.
As you can see from this brief overview, a forensic ballistics expert would need charts, reference books, and a fund of specialized knowledge just to handle the problem of class characteristics.
Individual characteristics complicate matters further. After the expert has examined his charts, stared at the bullet through his microscope, and told you that the round was fired from a Webley-Fosberry .455 automatic revolver, a question remains. Was it the same Webley-Fosberry that the prime suspect’s grandfather brought home after serving with Her Majesty’s Own Twelfth Grenadiers during the Boxer Rebellion? Or was it some other Webley-Fosberry?
When the bore is reamed out of the solid metal rod that is to become the gun’s barrel, the bore-reaming tool leaves behind a myriad of tiny scratches. Then comes the smoothing tool, which reduces these scratches to microscopic size, followed by the tool that cuts the grooves in the barrel and creates the lands. These too create their own pattern of scratches. And because each cut creates minute changes in the cutting tool itself, the metallurgical structure of each barrel is slightly different. So, even at the microscopic level each barrel leaves a different pattern of striations on the bullets passing through it. And two bullets fired through the same barrel in close succession (and before wear and tear, rust, or mishandling have significantly changed the barrel markings) should have very similar markings.
Shortly after 6 A.M. on September 27, 1927, the still-warm body of Police Constable George Gutteridge of the Essex County Constabulary was found on the Ongar Road just short of Howe Green. He had been shot four times, twice under one ear and once in each eye. These last two bullets were most certainly delivered postmortem. Gutteridge’s report book lay at his side, and he still clutched a pencil stub.
Scotland Yard was called in immediately, and Chief Inspector James Berrett took charge. Two of the murder bullets had passed through the constable’s body and were retrieved from the road surface; the other two were gathered at the autopsy. All four were .45 caliber.
An automobile tire print was found in the grass on the side of the road where Gutteridge had stood. His open report book and the fact that his flashlight was still in his coat pocket led Berrett to conclude that the constable was attempting to write by the light of an automobile headlight when he was shot. Had Gutteridge been writing down the license number of the car? Who would not want their license number written down? When Berrett asked whether any cars had been reported stolen in the area recently, he learned that a Dr. Lovell of the village of Billericay, twelve miles from the scene of the murder, was missing his car.
The murder of a local constable aroused a great deal of anger in the area. Leads poured in, all of which had to be followed up to make certain they were as baseless as Berrett suspected. Several locals suspected the same man, an eccentric who was believed to own a gun. He was quickly cleared. When a man in Basingstoke, sixty miles from the crime scene, confessed, police spent precious time interviewing him only to discover that he had a habit of confessing to murders he had not committed. He was cleared.
Dr. Lovell’s missing car was found by police in Brixton, a division in the south of London. Soil and grass found in the wheels on the left side of the car matched the grass on the bank of Ongar Road. Bloodstains identified as human were found on the running board. The car was examined carefully for fingerprints, but no useful ones were found. One spent cartridge case was discovered behind the left front seat.
The bullets retrieved from the crime scene were turned over to experts at the Royal Arsenal, who determined that they were fired from a Colt, a Smith and Wesson, or a Webley revolver. They then passed the bullets on to Robert Churchill to see if he could take the investigation further.
By 1927 Churchill was one of the leading forensic ballistics examiners in Great Britain. A gun maker by trade, he had taken over the business established by his uncle, Edwin Churchill, when Edwin died in 1910. Robert began his career by giving expert evidence in gun-related cases and in the process formed a friendship with Sir Bernard Spilsbury, the famous Home Office pathologist. This inspired him to expand his knowledge of guns beyond their mechanical characteristics and into bullet and shell comparisons and the other minutiae of forensic ballistics expertise. In 1927, having heard of Goddard and Gravelle’s invention, he had a comparison microscope built for his own use.
By looking at the bullets that had killed Constable Gutteridge through the comparison microscope and by further comparing them with rounds fired from various types of revolvers, Churchill declared with some assurance that the gun used in the crime was a Webley service revolver.
Now the police knew what to look for. “Acting on information received,” they staked out a garage in Battersea owned by Frederick Guy Browne, a man with a record of burglary, car theft, and violence. He was arrested on January 20, 1928, as he drove into the garage. In the driver’s side door pocket the officers found a fully loaded Webley revolver.
The next day Churchill ran comparison tests on bullets fired from Browne’s Webley and on the murder bullets. The comparison microscope showed a match, but the murder bullets were badly deformed—the similarity would be difficult for a jury to see. And because no British jury had ever been asked to accept the results of a comparison microscope identification, Churchill wanted his first case to be clear-cut. So he checked the shell casing found in the abandoned car against shells fired from the Webley and found that the breechblock markings on the Webley agreed with the pattern on the shell from the car. Churchill wanted to make it even more positive. He examined the breechblock patterns of the 1,374 handguns placed in the Royal Arsenal for repair and found that not one could be mistaken for the gun that had made the markings on the shell casing. Only then was he ready to go to trial.
On April 23, 1928, Browne and his accomplice, William Henry “Pat” Kennedy, went on trial at the Old Bailey. The forensic evidence clinched their conviction. They were hanged on May 31.
When Virginia police entered the house of Robert and Barbara Parks on February 18, 1950, they found Robert, a thirty-eight-year-old former army captain, in the bedroom. He was dead from a gunshot wound: a bullet had entered his right side, passed through his chest, and lodged behind his heart.
Barbara was twelve years younger than her husband. Robert Parks was known to have a violent temper, and for the past few years their marriage had been rocky. Just a couple of weeks before, Barbara had telephoned a friend in San Francisco in order to borrow the money for a one-way bus ticket. She wanted to leave Robert.
Barbara’s story, as she told it through hysterical sobs, was that she was in the kitchen when she heard a shot. Racing into the bedroom, she found Robert standing by the door. “Honey, the gun backfired,” he said, then fell dead.
The gun in question, an automatic pistol, lay against the far wall of the dining room. One shot had been fired, and the cartridge case had not ejected properly—it was jammed in the ejection port. By the angle of entry of the bullet into Parks’s body and the lack of powder stippling, the forensic investigators concluded that Parks could not have been holding the gun himself when it was fired. Barbara Parks was subsequently arrested for her husband’s murder.
But investigators had two questions to answer before winding up the case: Why would Barbara Parks tell such an improbable story when more plausible explanations were available to her? She might have claimed self-defense, or that she had mistaken her husband for a burglar, or that he was teaching her how to shoot when the gun discharged by accident. And how did the hot-air grille in the floor between the bedroom and the dining room get a dent that chipped the paint down to the metal?
The detectives wrapped up the evidence—the gun, bullet, cartridge case, and hot-air grille—and sent them to the FBI Crime Laboratory where technicians verified that the gun had indeed fired that particular bullet, which in fact had been encased in that cartridge. They examined the hot-air grille and saw that the dent in it matched two points on the slide and hammer of the automatic. Under a microscope they observed tiny flecks of paint from the grille at just those points on the gun.
As FBI technicians reconstructed the event, Parks threw the gun down in a fit of temper; the gun hit the hot-air grille at just the wrong spot and then fired. The bullet hit Parks—the angle of the entry wound was just right—and the cartridge case jammed in the ejection port as the pistol’s recoil bounced the gun along the floor.
The FBI sent a firearms expert to Virginia to testify to these findings. The judge ruled that Parks’s death was an accident. Barbara Parks’s incredible description of the events was in fact true. She was released from jail.
The Integrated Ballistics Identification System, or IBIS, is a system developed by Forensic Technology, a Canadian company, for the purpose of analyzing, storing, and sharing bullet comparisons and other ballistics information. In 1993 it was bought by the U.S. Bureau of Alcohol, Tobacco, and Firearms (ATF) at the same time the FBI was working on a system of its own called Drug-fire. Within five years the FBI abandoned Drugfire and worked out a deal with ATF for the shared responsibility of IBIS. Under their agreement, the FBI would provide and maintain the necessary communications network, while ATF would manage field operations.
IBIS is a sophisticated, many-faceted system. Using special IBIS equipment, the forensic examiner makes photographs of bullets or shell casings retrieved from a crime scene and enters them into the IBIS database along with background information—caliber, date of crime, date of entry, and rifling specifications. Using complex mathematical algorithms, IBIS then compares the newly entered data with its stored information. Candidates for matches are examined on a computer screen by a forensic examiner. If a comparison looks like a possible match, the actual physical evidence is then compared under a microscope as a final verification. An identification that links two or more different crimes is considered a “hit” and is assigned a special designation for future reference.
The National Integrated Ballistic Information Network program (NIBIN) has cross-connected IBIS into more than two hundred crime labs across the United States. Further, the IBIS system is used in over thirty countries worldwide. It is credited with developing thousands of leads that otherwise might have been missed.
In its quest to wring every possible bit of information from the bullets found at a crime scene, the FBI also developed a technique known as CABL, the Compositional Analysis of Bullet Lead. The theory was simple: most bullets are made of lead, or contain at least a core of lead inside a harder metal jacket. This lead contains impurities, elements that remain when the lead is refined or cast, as well as elements deliberately added to change the lead’s properties. (Antimony, for example, may be added to increase the lead’s hardness.) Furthermore, lead derived from ores mined in different locations will contain different impurities and in varying ratios. The additives of different bullet manufacturers will also vary in type and amount.
So, if you wish to connect a crime-scene bullet with a suspect and find that the bullet is too damaged or fragmented to compare it with a bullet fired from the suspect’s weapon, you can check the composition of the lead and compare it to the lead from bullets found in the suspect’s possession. If they are identical or very close, the FBI reasoned, the bullets probably came from the same batch of lead and possibly even from the same box of ammunition.
When the FBI began analyzing bullet lead in the 1970s, only three impurities were measured—antimony, arsenic, and copper. In 1990 more sensitive tests came into use, and tin, bismuth, silver, and cadmium were added to the list of detectable elements. The FBI believed that these tests were valid and useful, and their forensics experts testified to that effect in criminal trials. Like this, for example:
We can’t tell them apart. That tells us that they were manufactured or that they were likely manufactured in the same pot of lead at a bullet manufacturer. So out of the whole population of nine billion or so cartridges that are produced here in the United States, we can narrow it down to tens of thousands of bullets being produced that would have the same composition.
When over the years the FBI itself began to question these assumptions, it asked the National Academies to check their scientific validity. The Academies issued a report, Forensic Analysis: Weighing Bullet Lead Evidence, suggesting that the FBI had been perhaps too eager and that its conclusions were more positive than was warranted by the evidence. The Academies discovered, for instance, that bullet manufacturers regularly dump lead left over from one batch of bullet making back into the cauldron used for a new batch, significantly altering its chemical characteristics. Similarly, the castings of new bullets are dropped into vast bins before insertion into shells, so that bullets from one batch are easily mixed with bullets from another. Further, the chemical composition of a mass of molten lead can vary from point to point within that mass. And no consideration was being given to packaging ammunition from the same batches together; the report noted that the FBI identified bullets from fourteen different sources in one individual box. The report concluded:
CABL does not . . . have the unique specificity of techniques such as DNA typing to be used as stand-alone evidence. It is important that criminal justice professionals and juries understand the capabilities as well as the significant limitations of this forensic technique.