Crime Calif. 18-Year-Old Allegedly Killed Father, Teen Brother, Then Told Cops It Was a Murder-Suicide Police determined that Robert Cotter's account of the May 17 incident was inconsistent with the physical evidence By Chris Harris Chris Harris Twitter Chris Harris has been a senior true crime reporter for PEOPLE since late 2015. An award-winning journalist who has worked for Rolling Stone and MTV News, Chris enjoys prog rock, cycling, Marvel movies, IPAs, and roller coasters. People Editorial Guidelines Published on July 19, 2021 01:47 PM Share Tweet Pin Email Robert Cotter. Photo: Fresno Police Department A California teen who told police in May his younger brother fatally shot his father before turning the gun on himself was arrested Friday, charged with killing both victims, PEOPLE confirms. According to a statement from Fresno Police, 18-year-old Robert Cotter told police he was in the family's home on May 17 when his 15-year-old brother, Brian Cotter, shot and killed his 53-year-old father, Patrick Cotter. The defendant told detectives that immediately afterwards, Brian fatally shot himself with the same gun. Police were called to the home and discovered Patrick dead from a "gunshot wound to the upper body," and Brian alive, but severely wounded. Brian was rushed to the hospital, where he clung to life for several days before succumbing to his injuries. But as the investigation progressed, detectives determined Robert's account of the purported murder-suicide was "inconsistent with the physical evidence obtained during the investigation." Want to keep up with the latest crime coverage? Sign up for PEOPLE's free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases. Investigators confronted him, and the teen allegedly "made admissions, to detectives, about planning and acting out the brutal murders." Cotter is being held without bail. Police have not discussed a motive. Cotter is charged with two counts of murder. He has yet to enter pleas to the charges. It was unclear Monday if he was represented by an attorney.