Luke Woodham was found guilty Friday of killing two classmates--including a girl he had dated--during a shooting rampage at his high school.
It was the second time in two weeks a jury rejected claims the 17-year-old boy was insane. He had previously been found guilty of killing his mother just before the attack at Pearl High School and was sentenced to life in prison.
The Oct. 1 attack was the first of several high-profile school shootings around the country.
The jury, which deliberated about five hours, also found Woodham guilty of wounding seven other students during the shooting. He received two life sentences plus 20 years on each aggravated assault charge, all to run consecutively.
After the sentencing, Woodham again apologized to the victims and their families.
"I am sorry for the people I killed and the people I hurt," Woodham told the courtroom. "The reason you don't see any more tears is I have been forgiven by God.
"If they could have given the death penalty in this case, I deserve it."
Earlier Friday, Woodham testified that heartbreak over losing a girlfriend and fascination with occult rituals led to his mother's stabbing and his "reign of terror" over classmates.
"I'm so sorry. I'm so sorry," Woodham sobbed as he tried to explain why he opened fire with a hunting rifle at the school.
Woodham told jurors that after his breakup with Christina Menefee, 16, he fell under the influence of Grant Boyette, 19, a friend he described as both a mentor and a tormentor who introduced him to the occult.
"He told me I had to kill my mom," Woodham said. "He told me I had to get the gun and the car and go to school and get my revenge on Christy and cause a reign of terror."
Menefee and Lydia Dew, 17, died in the shooting attack after Woodham killed his mother, 50-year-old Mary Woodham.
Woodham testified against the advice of his defense team.
"I believe the killing of your dog, killing of your mother and shooting of the school--killing everything you love--is insane," said defense attorney Leslie Roussell.
Dist. Atty. John Kitchens said the jury had seen past the defense's "smoke screen" of insanity and done the right thing.
"Age is no excuse for murder in this country," Kitchens said.
Woodham had relied on the same insanity defense last week when he was found guilty of killing his mother.
Defense lawyers, as they did after his conviction a week ago, said they would appeal.
Two prosecution experts testified Friday that Woodham understood what he was doing when he opened fire with a hunting rifle inside the school.
Woodham said he did not want to kill, but Boyette had told him he would be "spineless and gutless" if he failed to act.
Boyette and several other alleged members of the cult-like group known as "the Kroth" have been charged with conspiracy in the school shootings.