Bradley Renfro’s defense attorney called a psychology expert to testify on the thirteenth day of the teen’s murder trial in Fairbanks.

Renfro is one of four teens accused of pistol-whipping, kidnapping and killing 16-year-old David Grunwald in November 2016. He was 16 years old at the time of his arrest.

Bruce Smith is a clinical and forensic psychologist based in Anchorage who specializes in adolescent brain development. Smith told jurors teenagers’ brains are “under construction” during those years and they’re often influenced by their peers.

“There are two concepts. One is an adolescent has immature choice or decision making and two is they are prone to risk-taking behavior when you compare them against adults,” Smith said.

Throughout the trial, Renfro has been described as a homeless teen whose father was an “active alcoholic.” Smith said the lack of parental figures can impact a person’s development.

“We all need mentorship in life. To the extent that we have good mentorship in our home, we have adults around us that make appropriate decisions,” Smith said.

Renfro’s attorney, Chris Provost, said that was the only expert he’ll be calling on behalf of the defense. He planned to call “civilian” witnesses on Tuesday.

Also on Tuesday, the state will call its lead investigator, Alaska State Trooper Sgt. Tony Wegrzyn, back to the stand to answer a few questions about his grand jury testimony from 2016. Then the state is expected to officially rest its case.

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