Cellebrite expert Ian Whiffin walked jurors through one of the most contentious pieces of evidence in Karen Read’s case Monday.

Jurors in Karen Read’s second murder trial heard more testimony Tuesday about location and temperature data recorded on her boyfriend’s cell phone the night she’s accused of killing him.

Karen Read pleaded not guilty to murder charges in the death of Boston police officer John O’Keefe and is facing a retrial after a jury was unable to reach a verdict last year. The trial is entering its second week as the prosecution continues to call key witnesses.