Two Massachusetts state troopers who investigated the death of a teenager prosecutors say was coaxed into killing himself through dozens of text messages from his girlfriend have testified the couple often discussed suicide.

The prosecution in Michelle Carter's manslaughter trial rested Thursday after hearing from the troopers and a pathologist in juvenile court in Taunton. Carter is charged in the 2014 death of 18-year-old Conrad Roy III but says her texts were protected free speech.

The pathologist who conducted the autopsy on Roy also confirmed that Roy died of carbon monoxide poisoning. Dr. Faryl Sandler testified that Roy had no alcohol or illicit drugs in his system when he died.