Corey Johnson, now 21, was sentenced to life by circuit judge Cheryl Caracuzzo on Thursday after he was convicted of first-degree murder and two counts of attempted murder last November.
On 12 March 2018, Johnson was staying at his friend Kyle Bancroft’s home for a sleepover when he stabbed 13-year-old Jovanni Sierra.
He also stabbed Mr Bancroft’s brother Dane and his mother Elaine Simon, who was also at the home then.
Ms Simon and Mr Bancroft sustained serious injuries but survived the attack.
While Johnson’s counsel wanted him to spend 40 years in prison, the court sentenced him to life.
“I don’t think rehabilitation is likely,” Ms Caracuzzo was quoted as saying by The Palm Beach Post newspaper.
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Police said Johnson had killed Jovanni because he had made an offensive remark about Islam, that Johnson had professed to following.
A police affidavit said Johnson attacked Sierra for idolising famous people as “gods,” which went against Islam, according to him.
He also said to police that he felt Dane Bancroft “made fun” of his faith.
The affidavit added that the Federal Bureau of Investigation had met one of Johnson’s friends in relation to a terror threat.
Court records said Johnson attacked Sierra after everyone had gone to sleep.
He also stabbed Ms Simon who had come upstairs after hearing noises while Sierra was being stabbed. He attacked Dane who tried to save his mother.
“I wish I could take it back. I wish I could do something to make this right,” Johnson said in court, according to NBC-affiliated news network WPTV.
“But I do want to apologise, not because it will change anything, but because I really, truly am sorry.”
He added that Sierra “was so young and had so much potential” in life.
“I am truly in disbelief that I could have done something so terrible. That’s not who I am, and I’m not a violent person.”
Johnson’s grandmother said in court that he had spent a lot of time alone as a child as his mother was under depression and abused prescription medications.
His attorneys pleaded not guilty, citing insanity for his actions and said he was manipulated by Isis propaganda videos online.
However, a psychiatrist said in court that in his opinion, Johnson knew right from wrong during his attacks.
A neuropsychologist diagnosed Johnson as a high functioning autistic with above average intelligence, delayed maturity and severe mental illness.