FAIRBANKS (AP) — Sound recorders worn by two slain Alaska State Troopers recorded evidence that suspects tampered with their service handguns, investigators testified Monday.

The investigators testified in Nenana at the trial of Arvin Kangas, 59, who is charged with evidence tampering and hindering prosecution in the May 1 deaths of Sgt. Scott Johnson and Trooper Gabe Rich outside Kangas’ home in Tanana, a village of 250 about 130 miles west of Fairbanks.

Tanana’s unarmed village public safety officer reported April 30 that Arvin Kangas drove without a license and pointed a shotgun at him. The Fairbanks-based troopers traveled to Tanana to arrest Kangas.

According to prosecutors, the officers confronted Kangas outside his home and he tried to go inside. As Kangas struggled with the officers, his son, Nathanial “Satch” Kangas, emerged from the home with an assault rifle and fired seven shots into the backs of the troopers.

Prosecutors contend that Arvin Kangas removed the fallen troopers’ service handguns from their holsters and cocked them to make it appear as if Nathanial Kangas acted to save his father’s life, the Fairbanks Daily News-Miner reported. They also say the father and son removed marijuana plants from the home.

Body recorders worn by the officers continued to operate after they died, Trooper Ramin Dunford, one of the investigators in the case, testified. The recorders picked up the sound of Johnson’s handgun being cocked, he said.

“I heard the slide of the service weapon coming forward and the racking of the other gun,” Dunford said. “One male voice refers to the other as ‘Dad.’ Then they leave after moving the plants.”

Dunford said he heard what sounded like Johnson’s pistol hitting keys on his duty belt. The belt was moved and twisted to the right, he testified.

Investigator David DeCoeur testified that officers first theorized that the slain troopers had been involved in a gunfight. Defense attorney Jim Cannon asked if the recordings changed DeCoeur’s mind.

“Absolutely. It’s clear it (Johnson’s gun) had been manipulated,” DeCoeur said.

Cannon asked whether DeCoeur thought Johnson had drawn his gun.

“I know he didn’t,” DeCoeur said.

Portions of the audio recordings were played for jurors.

Prosecutors rested their case after the testimony. The trial was to resume Tuesday afternoon.

Nathanial Kangas, 21, is scheduled for trial in November.