The Portland Police Department is under scrutiny for using the encrypted messaging app Signal, which deletes messages within 24 hours, during investigations and stakeouts.

The Portland Press Herald reports the practice has raised legal concerns, with Cumberland County’s top prosecutor saying the use of Signal raises questions about “whether something is being hidden””

There’s also concern the use of the auto-delete function sets a dangerous precedent.

Portland Police Chief Mark Dubois defends the use of the app, saying it provides secure communication in certain circumstances where sensitive information is involved.