(CNN) -- Prosecutor Jim Flaiz, upon learning Ohio school shooter T.J. Lane was going to make a statement in court Tuesday, told relatives of his victims to be prepared for something inflammatory.
Lane's own lawyer told the court he urged his client not to make the type of statement that the attorney expected to be delivered.
But no one could have fully foreseen the actions and words of Lane, who entered the courtroom and removed his blue button-down shirt while the judge and those in attendance took their seats.
Lane, now 18, revealed a white T-shirt with the word "killer" written on it.
The attire was similar to what he was wearing when arrested by police shortly after the February 27, 2012, killings at Chardon High School in northeastern Ohio.
Given the opportunity to speak a few minutes later, Lane made an obscene gesture at the victims' families and spoke to them briefly, using explicit language.
"What he did was beyond anything I could envision seeing in a courtroom," Flaiz told CNN a few hours after a judge ordered Lane to spend the rest of his life in prison without parole. "I was shocked and disgusted at how the defendant conducted himself."
Lane smiled and smirked during much of the hearing, laughing when Flaiz described him as an "evil person."
According to the Geauga County prosecutor, Common Pleas Judge David L. Fuhry was unaware that Lane had the lettered T-shirt. "I think everyone felt the effect of that shirt at the same time," said defense attorney Ian Friedman, according to CNN Cleveland affiliate WJW. Friedman said he, too, had no advance knowledge of the T-shirt.
Lane pleaded guilty last month to three counts of aggravated murder, two counts of attempted aggravated murder and weapons-related charges.
The death penalty was off the table because of Lane's age at the time of the crimes, according to prosecutors.
For their part, victims' relatives kept calm and made their own statements, describing the pain they felt and the profound loss to both themselves and the community. They also cited the contributions of their killed or wounded loved ones.
"I was very proud of the family members in the courtroom," said Flaiz, adding he was not sure he could have kept his composure if he were in their shoes.
The mother of a wounded student now confined to a wheelchair looked directly at Lane as she told him he was fortunate so many officers were in the small courtroom.
"Because of you, our town will never be same," Holly Walczak said. "Why? Why did you do it? Why?"
Walczak said she has watched her son, Nick, suffer daily in the year since he was shot in the school cafeteria and in the hallway when he was pursued by Lane.
"You are evil. I will have to eventually forgive, otherwise you will haunt me," she told Lane.
Demetrius Hewlin, 16, died from his wounds.
His brother, Philip Carter, read a statement in court on behalf of mother Phyllis Ferguson.
"In our humanity, we still cannot understand why his life was taken in such a violent manner," said Carter.
Authorities allege that Lane walked up to a table in the Chardon High School cafeteria and started firing.
When the violence ended, six students had been shot, and in the following days, three died: Daniel Parmertor, 16; Hewlin; and Russell King Jr., 17.
T.J. Lane was known by many around Chardon High, 30 miles east of Cleveland. But at the time of the shooting, he was there to be transported to Lake Academy Alternative School in nearby Willoughby.
Lake Academy describes itself as a school for "at-risk" students who are "reluctant learners" struggling with problems such as substance abuse and mental health issues.
After the shooting, an assistant football coach chased Lane out of Chardon High, and police arrested him nearby a short time later.
Parmertor's mother, Dina, last year told CNN's Anderson Cooper her son was a jokester "everyone wanted to be around." Daniel had just started a job at a local bowling alley.
"My heart is broken. It is torn apart. .. I want people to know him," said Dina Parmertor. "They did not know the joy of knowing him."
Tuesday, she looked at Lane and called him a "weak, pathetic vile coward."
"If I had my choice you would die an extremely slow, torturous death," the mother said.
Before he sentenced Lane to consecutive sentences of life without parole and additional sentences totaling 37 years, Fuhry said the former student showed no remorse, feigned mental illness and seemed determined to make "front-page news."
"A school is a place where a student should feel safe," the judge said, adding Lane took advantage of unsuspecting students. "These juveniles were ambushed."
Fuhry said Lane would be a danger if he were ever released.
King's sister, Crystal, called Lane a "monster." Her brother was a compassionate blood donor who tried to become a friend of Lane because "he felt sorry for him."
After the sentencing, defense attorney Friedman said Lane's comment to the families was a "very difficult statement to hear."
Lane's sister, Sadie Lane, pleaded for compassion and prayers for her family a well as for those of the victims. She, too, was in the school cafeteria when the rampage began.
"Many families were damaged that day. Our family was, too," she said.
While the judge indicated Tuesday there was no known motive for the attacks, Flaiz said his office has a theory it would have presented if the case had gone to trial. He declined to elaborate, saying he will meet with victims' family members in the next week.
"I got a sense from the families they wanted to hear why he did it and they wanted to hear remorse," Flaiz said.
Residents have come together since the shootings, the prosecutor said. "Sometimes it takes a tragedy for everyone to realize how close-knit a community we have."
"In the end, everyone is sad. It is an incredibly sad situation."
CNN's Ben Brumfield, Stephanie Gallman, Tanika Gray, Aaron Cooper and Jason Hanna contributed to this report.