Crush - Alan Jacobson [120]
Brix cleared his throat. “I’ve asked Austin Mann and Burt Gordon to stay on with us a bit longer, even though their work on the arson is largely done. We can use the manpower, and I’d rather not bring in fresh bodies that have to get up to speed. Hopefully we’re closer to catching this UNSUB than we think.” He extended his right arm and indicated the visitor. She rose from her chair and walked to Brix’s side.
“This is Amanda Sinclair from AirCom Consulting. Amanda’s here to explain text messaging, and give us a handle on how we can track, and hopefully apprehend, the UNSUB next time he contacts Karen.” He moved toward his seat. “Amanda.”
The woman, early thirties with frosted brown hair, took the center stage. “I know you’ve all used text messaging, or what we in the industry call SMS, or Short Messaging System. We don’t think much about those little notes we send each other. But they can be useful in law enforcement if we know how to use them. And if the criminal doesn’t. I think it’s important for you to know what we can’t do, as well as what we can do.
“So here’s the crash course. And I’m leaving a lot out, so if you’ve got a question, don’t be afraid to ask.” She opened a file and set out some papers. “The texts that go through a wireless provider’s system are not viewed by the carrier. They don’t read them—they simply store the technical transmission information for varying periods of time. Very few carriers actually store the ‘text’ of text messages. The storage space required, multiplied by the billions of texts exchanged between users, is staggering.”
“How long do they keep this transmission information?” Lugo asked.
“Good question. The answer depends on the carrier. Basically, there are several different systems for storing message information. The two most common are CDR and SMS Center. In CDR, or Call Delivery Records, the information is stored for seven days. These CDRs list information such as the time stamp—year, month, day, hour, minute, second, character length—and a variety of other technical info. The International Mobile Subscriber Identity, or IMSI, is also stored; it’s like a thumbprint for the SIM card that houses all the phone’s user specific information. You all know what a SIM card is, right? It’s a little flash memory chip that fits into certain phones. You pull the card out of your old phone, slip it into a new one, and you’re ready to go, without having to reenter all your contacts and such. With me so far?”
“Go on,” Brix said.
“We also store the IMEI, or International Mobile Equipment Identity, a unique thumbprint for the exact phone equipment that’s used. But it’s got no permanent relationship to the individual subscriber. It’s mainly used to identify valid users of the network, so if the phone is stolen, the carrier can shut off that IMEI and the phone will be a useless hunk of metal and plastic.
“The other commonly used system is the SMS Center, which is the E.164 address that lets everyone know which carrier the SMS is originating from or terminating to, the phone number the message is being sent to, how the digits were dialed, and so on. Here’s an example.” She moved to the overhead projector, set one of her pages on top, and turned it on. A document that resembled an Excel spreadsheet was displayed. A bar at the top read, SMS Center Log Window.
Everyone studied the screen. Vail and Lugo were taking notes as Amanda oriented the task force members as to what they were seeing.
“Any questions?” she asked.
“You said there are other ways of storing messages,” Lugo said.
“Yes. Another common method is called SMSC, or Short Message Service Center. It shows where the messages originate and terminate from a carrier’s system. This info is kept for a period of time based on message capacity. Sometimes, if there’s a lot of messages, they’ll only have the data for a week. Other times they may be able to go back a month.”
Amanda slipped a different page onto the