Nikolas Cruz pleaded guilty Wednesday to 17 counts of first-degree murder and 17 counts of attempted first-degree murder for killing 17 and injuring 17 others in the Parkland, Florida, school shooting.
Cruz replied "guilty" when Judge Elizabeth Scherer asked how he wanted to plea to the slaying or wounding of each victim.
Parents of the slain students watched from the courtroom and wiped tears from their eyes.
Cruz said in court, "I am very sorry for what I did and I have to live with it every day. … It brings me nightmares and I can't live with myself sometimes."
Cruz said he believes the victims should be the ones to decide whether he gets the death penalty.
A jury will decide if Cruz, 23, will get the death penalty or life in prison.
A prosecutor gave a timeline of the massacre, including Cruz's Uber ride to the school, which classrooms he fired into and who was shot when.
Manuel Oliver, father of 17-year-old victim Joaquin Oliver, told ABC News Live on Wednesday, "No one told me with details -- how my son was shot first and then was reshot two more times, so maybe he was still alive. That means that he was suffering a lot."
On Feb. 14, 2018, Cruz, then 19, gunned down 14 students and three staff members at his former school, Marjory Stoneman Douglas High School. He was taken into custody that day.
Last week Cruz pleaded guilty to charges in connection to his attack on a jail guard in 2018.
Jury selection for the penalty phase will begin on Jan. 4.