A former college student who confessed to killing his father with his Cub Scout knife in their Freeport home entered an insanity plea Tuesday in the murder case against him.

Jordan Johnson, 25, pleaded not responsible by reason of mental disease or defect in the December 2015 slaying of his father, Russell Johnson, 55.

In a calm voice, Jordan Johnson told state Supreme Court Justice William Donnino he was entering the plea of his own free will. It followed a filing by the defense earlier this year that said Johnson had “a long, well documented history of mental illness,” specifically paranoid schizophrenia, and also abused cannabis.

That court record said the defense intended to present psychiatric evidence at trial that at the time of the crime Johnson “lacked substantial capacity to know or appreciate either the nature and consequences of his conduct or that such conduct was wrong.”

Johnson’s plea in Nassau County Court followed separate psychiatric exams that mental health professionals for the defense and prosecution performed. After noting those psychiatric reports, the judge accepted Johnson’s plea in the interest of justice.

Johnson’s attorney, Douglas Stern, said after court that authorities would commit his client shortly to the custody of the state Office of Mental Health for an evaluation. The Lake Success lawyer said there then would be a hearing to determine Johnson’s level of dangerousness.

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In such a case, a judge then decides if an individual needs confinement in a psychiatric facility, and the level of security required, or if that person can be released, an OMH official said Tuesday.

After 18 months of confinement, a patient’s future status generally is evaluated every 2 years, according to the state agency, which said a court order is required for a patient’s release.

Court records show the younger Johnson met a Freeport police officer at his family’s front door on Laurette Lane after a response to a 911 call shortly before 4 p.m. on Dec. 29, 2015, about a possible dispute between a father and son involving a knife. He then told the officer: “I killed my father,” his court file says.

Police found the victim, a longtime CBS employee, in a bedroom and noted blood stains on his son’s clothing, socks and boots.

Jordan Johnson spoke repeatedly to police, including telling them he left the knife he used to stab the victim by the bed, according to court records. They say he also told a detective that while he may have had problems with his father, the man “didn’t deserve this.”

In a written statement, the son described having an argument with his father before the fight turned physical. He said he tried to hold his father down on the floor of his bedroom, but his father was stronger.

The son said he was able to get away from him, and that his aunt from North Carolina called and he told her to call the police. The younger man said the fight continued before he put his father in a headlock.

“I began to get scared at this point. I then grabbed a Cub Scout knife that I had next to my bed and stabbed my Dad three times,” Johnson told police.

The 2009 Freeport High School graduate had attended SUNY Binghamton. But a cousin has said previously that Johnson left his college studies behind and returned home.

Relatives and neighbors have said the young man’s appearance and behavior changed drastically a few years before his father’s slaying. The Freeport man’s family declined to comment while leaving court Tuesday.

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After Russell Johnson’s death, an anchorman on “CBS This Morning” paid tribute on air to a man he said spent decades at the network, working most recently in a division that coordinates video for that show’s news segments.