Kip Kinkel, who killed his parents before murdering two of his classmates and injuring another 25 in a 1998 school shooting in Oregon, has said that he feels “tremendous, tremendous shame and guilt” in his first interview.

Kinkel, now 38 years old, spoke with HuffPost for 20 hours over the course of 10 months while serving a 111-year sentence at the Oregon State Correctional Institution.

He committed the crimes at the age of 15 while suffering from an undiagnosed case of paranoid schizophrenia.

He told HuffPost that he didn’t only feel guilty for the crimes he committed but also the effect his actions has had on young offenders being sentenced to life in prison.

His case has been used by some of the victims of the Thurston High School shooting and others to work against reforming juvenile justice in Oregon.

He has remained silent until this point because he didn’t want to further traumatize those affected by his crimes but he also felt that his silence was hindering those young offenders from getting a second chance.

“I have responsibility for the harm that I caused when I was 15,” Kinkel told HuffPost. “But I also have responsibility for the harm that I am causing now as I’m 38 because of what I did at 15.”

Kinkel spoke about how he had been hearing voices since he was 12 years old, becoming fixated on weapons such as knives, guns, and explosives. He thought China was going to invade the United States and that the government along with Disney had put a microchip in his head.

He said his “whole world blew up” when he was caught at the high school in Springfield on 19 May 1998 with a handgun that he had bought from a fellow student.

“All the feelings of safety and security – of being able to take control over a threat – disappeared,” he said.

Under the threat of being expelled, being charged with a felony, and with a sense of shame, he said the voices in his head convinced him he had to kill his parents and then return to the school to “kill everybody”.

Killing his parents the following day, he went to the school on the day after that and killed Ben Walker, 16, and Mikael Nickolauson, 17, and injured 25 people before he was overpowered by other students.

Not wanting to accept his diagnosis and plead not guilty because of insanity, he instead pleaded guilty to resolve the case quickly, feeling pressure from the community.

“I feel tremendous, tremendous shame and guilt for what I did,” Kinkel said “I hate the violence that I’m guilty of.”

Kinkel’s attorneys filed a petition in federal court in March, contending that his guilty plea was not made voluntary, having been off his medication for weeks. The lawyers also argued that his sentence was unconstitutional.

“Sentencing a juvenile to die in prison because they suffer from a mental illness is a violation of the Eighth Amendment,” his attorneys wrote.

The Oregon Legislature passed a measure in 2019 to stop automatically sending 15- to 17-year-olds to adult court for certain crimes and to make sure that they’re not sentenced to life in prison without the chance to seek parole.

A month later, legislators passed another measure to clarify that the rule change was not retroactive after critics worried that the new law could lead to Kinkel’s release.

In a video released in 2019, Adam Walker, the brother of victim Ben Walker, said: “It doesn’t matter if he was 15. The victims don’t get second chances. Why should the offenders?”

Kinkel said he watched the debate play out from prison.

“It was like, there was hope,” he said. “And then the Legislature… came back and said, ‘No, we are specifically, intentionally, purposely with everything that we have, going to take this away from the kids already in the system.’”

He said he tries to avoid thinking of ever getting out.

“I don’t allow myself to spend too much time thinking about that because I think that can actually bring more suffering,” he said.