A California teen accused of fatally stabbing a 9-year-old boy confessed to the crime on Monday, the Contra Costa Times reports, telling the paper he wanted to experience the act of killing before the impending end of the world.

“I wanted to see what it was like to take a life before someone tried to take mine,” 18-year-old William Shultz reportedly told the paper.

According to police, Shultz was a friend of the victim’s family and was staying at the third grader’s home at the time of the murder. From CBS News:

He told the paper that his family had been concerned about his odd behavior and mental health over the last month and that he was briefly hospitalized Saturday in a county facility. He said a doctor discharged him and sent him in a cab to his mother’s home where a fight between he and his mother ensued. He says that’s why he went to spend the night at the victim’s home. Schultz and the victim’s older brother have been friends since 6th grade.

Sheriff’s deputies were called to the victim’s house at about 10 a.m. Sunday but the boy’s family had whisked him to the hospital before authorities arrived. The boy was pronounced dead at the hospital.

Shultz was arrested later that day after seeking treatment for his own injuries at a nearby hospital. On Tuesday, prosecutors filed first degree murder charges against Shultz.

“This wasn’t a random act,” Sheriff’s Lt. Ken Westermann told the San Francisco Chronicle. “This wasn’t some sort of stranger that came into the home and murdered a child. This was a family friend.”

[Image via Contra Costa County Office of the Sheriff]