CHARDON — Wearing a T-shirt with “killer” scrawled across it, a teenager cursed and gestured obscenely as he was given three life sentences Tuesday for shooting to death three students in an Ohio high school cafeteria.

T.J. Lane, 18, had pleaded guilty last month to shooting at students in February 2012 at Chardon High School. Investigators have said he admitted to the shooting but said he didn’t know why he did it.

Before the case went to adult court last year, a juvenile court judge ruled Lane was mentally competent to stand trial despite evidence he suffers from hallucinations, psychosis and fantasies.

Lane was defiant during the sentencing, smiling and smirking throughout, including while four relatives of victims spoke.

After he came in, he calmly unbuttoned his blue dress shirt to reveal the T-shirt reading “killer,” which the prosecutor noted was similar to one he wore during the shooting.

At one point, he swiveled around in his chair toward the gallery where his own family members and those of the slain teenagers were sitting and spoke suddenly, surprising even his lawyer..

A student who was wounded in the rampage dismissed the outburst.

“He said it like a scared little boy and couldn’t talk slow enough that anyone could understand him,” said Nate Mueller, who was nicked in the ear in the shooting.

Dina Parmertor, mother of victim Daniel, called Lane “a pathetic excuse for a human being” and wished upon him “an extremely, slow torturous death.” She said she has nightmares and her family has been physically sick over the crimes.

“From now on, he will only be a killer,” she said, as Lane’s smile widened. “I want him to feel my anger toward him.”

Prosecutors say Lane took a .22-caliber pistol and a knife to the school and fired 10 shots at a group of students in the cafeteria. Daniel Parmertor and Demetrius Hewlin, both 16, and Russell King Jr., 17, were killed.

Lane was at Chardon waiting for a bus to the alternative school he attended, for students who haven’t done well in traditional settings.

Six days before the rampage, Lane had sent a text message to his sister, who attended Chardon High school, and mentioned a school shooting, Geauga County Prosecutor James Flaiz disclosed after the sentencing. He gave no details about what the message said.

“The way the text message was phrased to his sister, I’m not sure she would have taken it as anything. I think only when you look at it in retrospect does it really have the impact that it does now,” Flaiz said.

Lane’s sister, Sadie, was in the cafeteria the day of the shooting, and said outside the snow-swept courthouse that the brother she saw in court wasn’t the one she remembers. She asked for prayers for her family.

“It may be hard for some to understand, but I love my brother and hope that whatever the sentencing in life takes him in the future, that he can touch others’ lives in a positive way from the point of view that only he can give,” she said.

She spoke and left the courthouse before Flaiz addressed reporters.

Flaiz said he has a theory about the motive but wouldn’t discuss it until he has a chance to meet with the families of victims and answer their questions.

Lane’s courtroom behavior came as a surprise, he added.

“ I am totally disgusted by that,” Flaiz said. “What he did today is consistent with what we thought of him all along.”

One of Lane’s defense attorneys, Ian Friedman, also said he was caught off-guard by the comments. The defense had signaled earlier that Lane wouldn’t speak in court and didn’t want anyone to speak for him.

Lane had pleaded guilty last month to three counts of aggravated murder, two counts of attempted aggravated murder and one count of felonious assault.

Life imprisonment without parole was the maximum sentence Lane faced. He wasn’t eligible for the death penalty because he was 17 at the time of the shootings. Relatives of the slain students indicated earlier they wanted Lane to get the maximum sentence.

In addition to three life sentences without chance of parole, Geauga County Common Pleas Judge David Fuhry also gave Lane sentences totaling 37 additional years for attempted murder and felonious assault and using a weapon in the crimes.