48: Nash pressed the End Call button on his phone and dropped it back into his pocket. “I’m getting nothing but voice mail for Sam. His line’s not even ringing.”
Klozowski didn’t look up. His gaze was fixed on his center monitor, a 27-inch surrounded by four 22-inch screens.
Nash felt like he could get a tan standing here. Although Kloz had his laptop in the car, he insisted he could analyze the data faster at his desk at Metro.
“You said we shouldn’t call him,” Kloz said in a distant voice as he scrolled through text. “He made his bed and all that.”
Nash pulled his phone back out of his pocket and dialed Porter’s home number. “It’s not like him to go silent.” Four rings, then an answering machine picked up. He hung up. “Maybe we should swing by there.”
“I think I’ve got something.” Kloz studied the screen.
Nash leaned in, carefully avoiding the Batman memorabilia and candy bar wrappers scattered haphazardly around Klozowski’s desk. The screen was filled with strings of numbers and letters paired off, separated by colons. “What am I looking at?”
“See this here?” Kloz pointed at a series of dates. “Notice how the data starts on February ninth?”
“Yeah.”
“Well, the data should go back much further than that. Months, maybe years. The data writes to this file until it runs out of room, and then old data is purged for new data. Thing is, they never run out of room.”
“So if it starts on February ninth, that means our unsub wiped the file like he did at the Reynoldses’ house, right? So we’ve got nothing?”
Kloz pointed at the screen with a pen. “We’ve got something. See this first one?”
He indicated a line that read:
02-09-2015 21:18:24 a8:66:7f:04:0c:63
“The first part is the date, the second part is the time, and this last section is a Mac address. I combed through the entire file, and this particular Mac address only appears one time—right here, the very first entry,” Kloz explained.
“What does that mean?”
“I think our unsub wiped the router data and disconnected, but not before the new log recorded his or her presence for one second. I’ve accounted for all the other Mac addresses listed during this forty-eight-hour period. Every one ties back to a device at the house but this one.”
“Can you trace it?”
Kloz shook his head. “Sort of. The ID is unique to this computer. Mac addresses are built into the hardware so nobody can change or modify the string, but you can’t trace it across multiple networks to find a current location. Not like an IP address, anyway.”
Nash let out a sigh. “Then how does this help us?”
“It’s still a bit like a fingerprint,” Kloz said. “I ran this unique Mac address through the data we pulled from the Starbucks and found a record in the log. The unsub was connected to that network for a total of thirty-three minutes with the same computer.” Kloz leaned back in his chair. “Chicago has a pretty hefty public Wi-Fi system. We’ve got towers in the parks, the libraries, the trains—they’re everywhere. On February twelfth, this same Mac address connected to the public system at Jackson Park for nearly an hour and a half in the morning.”
“When he hid Ella Reynolds in the water.”
Klozowski nodded. “The activity appears to be passive, occurring at intervals rather than randomly. This tells me the unsub probably had his laptop in the truck we saw on that video, but he didn’t actually use the computer. The traffic I found is most likely automated tasks like e-mail, just his computer working in the background. One hit every minute. If he had actually used it to browse the web, we’d see more random hits.”
“Why would he connect to the Wi-Fi and not use it?”
“I don’t think he purposely connected this time,” Kloz said. “Most likely, he connected the laptop to the public network at some time in the past and didn’t delete the connection. By leaving the entry in the system, his computer would automatically connect whenever he’s in range of that same network again, like mine did at Starbucks. It’s a time saver. In this case, anytime he’s within range of the city Wi-Fi.”
“So back to my original question—can you trace it?”
“Back to what I said earlier. An IP address is a bit like a landline telephone installed at a house. The number is always the same and always on, so it can be traced back to a static physical location. A Mac address is specific to the device, in this case a laptop. That laptop can be switched on or off and connect to a million different networks. It can move from one to the next or go dark for an indefinite period of time. This means we can’t trace it, but we can watch for it.”
“How?”
“When the city planners rolled out free public Wi-Fi, they built in a backdoor for law enforcement. I can write a bot and put it out there. If our unsub’s laptop connects to the public system, we would be alerted. At that point, we’d be able to narrow his location down to the specific hub he’s attached to. That’s going to be a much wider grid than an IP would give us, though—the towers have about a quarter-mile radius.”
“A quarter mile of city blocks might as well be different countries,” Nash said.
“We’ll know where he is in the city. It’s a start. Maybe we’ll get lucky and it will cross with something else.”