Northeastern expert Gary Cantrell says cellphone and other electronic evidence are considered circumstantial but can help build a case.
Will the cellphone of Boston police officer John O’Keefe help clear Karen Read, the girlfriend accused of running him over with her SUV and leaving him for dead in the snow?
Or will this week’s testimony by a digital forensic specialist that the phone remained immobile outside the house where Read dropped O’Keefe off until his body was found frozen hours later sink the defense argument that she was framed?
Electronic evidence is doing a lot of the talking as Read’s murder trial unfolds in a Massachusetts courtroom.
Such evidence can be a powerful tool in criminal cases, says Northeastern associate teaching professor Gary Cantrell, who has an extensive background in using digital forensics for law enforcement.
Electronic data revealed by digital forensics tends to be used more often to help build a case than prove a case on its own, says Cantrell, who hasn’t followed the Read case.
“Digital evidence in general is only circumstantial,” he says. “It’s very useful and it’s supporting information, but it’s still not something you typically hang an entire case on because there are too many ways to poke holes in the information.”
Digital information includes anything that leaves a digital footprint — from an eReader, TV, computer, game playing station, cellphone or fitness watch, Cantrell says.
It rises to the level of digital forensics when it meets rules of court admissibility, he says. It involves taking the information, verifying it, creating an exact binary duplicate and using something called “hash values” to confirm the duplicate’s authenticity.
For those who do not know about the case from the first trial, which ended in a hung jury in 2024, prosecutors say Read ran over O’Keefe during a drunken quarrel outside a friend’s house and drove off, leaving O’Keefe unconscious in the snow where he was found dead the next morning.
The defense argues that she was framed and that O’Keefe was beaten up inside the house belonging to a fellow Boston police officer, attacked by a dog and then moved outdoors in the cold.
This week a digital forensics specialist testified that O’Keefe’s cellphone remained in the front yard of the house where O’Keefe was dropped off around 12:30 a.m. until his frozen body was found before 6 a.m. That testimony could bolster the prosecution. However, defense attorneys challenged the testimony on cross examination.
Using cellphone data to determine location “is not an exact science,” Cantrell says.
“It’s not like I can tell exactly what room your cellphone was in, but I can probably tell that it was at your residence,” he says.
“It’s the communication of the phone with the tower” that indicates location, Cantrell says. “The way that cell networks work is as you’re traveling they hit multiple towers to send the data packets back and forth for communication. If they’re hitting at least three towers, you can triangulate your position.”
“Your phone has a unique ID associated with it, and once your provider reveals who that ID belongs to, law enforcement can work in conjunction with that provider to see which towers have been hit and do a little bit of simple math to figure out where that device was at,” Cantrell says.
“I can tell you were in a specific neighborhood. Telling whether you are inside the house or outside the house might get a little bit more tricky. The more precise that you want to be, the harder that gets,” he says.
“Hopefully, they did some tests,” Cantrell says. “They would need the phone’s make and model. There’s other factors, too.”
The other issue, he says, is that “I can only tell where your phone has been. They can’t tell where you have been personally without additional corroborating evidence. There’s no way to say 100% that this device was on your person whenever you went from point A to point B.”
If a photo is taken of a person at a certain location, that moves evidence beyond the circumstantial category because the taking of the photo triggers GPS coordinates that are proof of location, Cantrell says.
“It’s going to come down to what the judge and jury decide” after evaluating testimony from the prosecution and defense, Cantrell says.
Electronic data unearthed by digital forensics “should be additional information for them to consider.”
“It shouldn’t be damning, and it shouldn’t be exculpatory either,” Cantrell says.