Portland police say their use of a controversial messaging app that can be set to automatically delete text messages is in line with Maine law. But some city councilors, legal experts and attorneys say they’re concerned about the potential repercussions of officers using the app during operations that may result in criminal prosecution.

Messages acquired this month by the Portland Press Herald through a public records request revealed that some officers use the encrypted, publicly available app Signal to communicate with one another during investigations and apparent stakeouts.

A bulk of the messages appeared to be missing from some of the text threads obtained, and officers changed some group chats to delete messages within a short time frame after the records request was submitted. Signal doesn’t default to deleting messages, but users have the option to erase their messages automatically — from either seconds to weeks after they are sent.

The county’s top prosecutor, two prominent defense attorneys and multiple city councilors said this week that the department’s use of the auto-delete option raises important questions about proper retention of public records and discovery in criminal cases — and whether evidence is possibly being hidden.

Police Chief Mark Dubois said in a statement that the department does retain messages they need to under Maine law and department policy.

Mayor Mark Dion said he trusts that Dubois and his officers will do what’s required of them, so he isn’t personally concerned about their use of the app. Still, he and other councilors are eyeing a council or committee-level review of the issue.

IN THE COURTROOM

Dubois wouldn’t clarify this week why officers have the auto-delete function turned on in some cases, but he contends that the department is retaining relevant messages that would be subject to Maine’s public records law and its other legal obligations to retain information.

Some legal experts say letting officers determine which messages should be saved could cause problems.

Thea Johnson, a professor at Rutgers Law School, said figuring out what evidence is important often becomes clear as an investigation proceeds. That could mean that conversations about a suspect that may have seemed irrelevant while police were doing their work could later be a crucial detail in a trial.

Jonathan Chapman, who teaches criminal law at the University of Maine School of Law, said police’s use of Signal could be potentially problematic because of their obligations under discovery laws, including disclosing any exculpatory evidence — that is, evidence that could be favorable toward a defendant.

Some Maine defense attorneys have said they’re not surprised that police are using Signal, but they contend that officers appear to be circumventing Maine’s discovery rules by deleting messages.

Tina Nadeau, director of the Maine Association of Criminal Defense Lawyers, said it’s already hard enough to obtain police text messages and other communications, so it’s especially frustrating to her that officers are choosing to delete other communications that could be useful in court.

“How do we believe in the word of an officer who, as a matter of course, deletes communications with other officers?” she asked. “If I was a supervisor, I’d be very concerned about that. Because how do you put officers on the stand if they’re engaged in the intentional deletion of information?”

EYEING A CITY REVIEW

City Councilor Kate Sykes said she understands the need for police to communicate securely, but that law enforcement officers have been doing the same work for decades and have never needed tools that erase the public record.

“If our current tools aren’t meeting operational needs, then the answer is to improve those systems, not to move public business onto platforms designed to disappear,” she said. “I mean, we’re not in a spy movie here.”

At a minimum, Sykes said, Portland should review its policies to make sure they are being followed and are keeping pace with evolving technologies. She suggested the city seek guidance at the state level, “so municipalities aren’t each trying to solve the same problem independently.”

Councilor Pious Ali said he’s trying to better understand how Signal is being used and whether the department is complying with public records requirements. He also supports a council or committee review.

“Maintaining trust between the public and the police, as well as across our municipal institutions, is critical,” he said. “Transparency and accountability are key to sustaining that trust.”

Dion said he’s suggested that the Health and Human Services & Public Safety Committee discuss the issue in April, when members are already slated to host Dubois regarding the department’s communication with federal immigration authorities.

Sarah Michniewicz, who serves on the committee, said she’s looking forward to hearing from the chief at the meeting to better understand how the police department is using Signal.

“There are legitimate uses for encrypted texting in certain police operations, and I think it’s important for the police to do so when necessary — and for the public to be able to trust that the technology is being deployed appropriately,” she said. “Auto-deleting texts undermines that trust, and I’m concerned that an officer chose to enable that function after a request for records had been made.”

RETAINING RECORDS

Dubois has said his officers use the app as a secure, “supplemental communication tool” like a text message, phone call or radio transmission.

Johnson, the Rutgers professor, said while texts feel like casual conversation similar to talking with a friend, the rules of evidence make it clear that written communication should be treated differently.

“If you’re using regular texting apps, then that stuff all gets saved,” Johnson said. “If it gets saved normally and one has the right to have access to it, then you should have access to it. They should have to hold onto it.”

She said police nationwide are increasingly using emerging technologies like Signal and artificial intelligence, prompting communities across the country to figure out how they should fit into their existing criminal justice system.

“What we see over and over again is that the law has trouble keeping up with technology and the way people use technology,” Johnson said.