Nikolas Cruz pleaded guilty on Wednesday to 17 counts of murder in relation to the 2018 shooting at Stoneman Douglas High School in Florida. The 2018 shooting was the deadliest school shooting in US history.

The pleas begin the sentencing hearing, which will determine whether the 23-year-old will face life in prison without parole  or face the death penalty. The prosecution has not moved away from seeking the death penalty since the proceedings began.

In 2018, Cruz killed 17 people and injured 17 others at Stoneman Douglas High School. Cruz fled the scene by blending in with fleeing students. He was later arrested without incident at the nearby city of Coral Springs. Cruz was charged with 17 counts of preempted murder and 17 counts of attempted murder.

The shooting occurred during a period of heightened public support for gun control measures following mass shootings in Paradise, Nevada, and Sutherland Springs, Texas. Survivors and students from Stoneman Douglas High School organized and formed Never Again MSD to promote the adoption of gun control policies in the state.

There was heavy criticism of the poor response by the local sheriff’s department that responded to the shooting. The department failed to follow up on reports of Cruz’s threatening behavior, and failed to intervene on the day of the shooting, choosing instead to remain outside the school. Florida Governor Ron DeSantis eventually suspended the head of the responsible department, Scott Israel, over the department’s failures on the day.

The case is expected to go to the penalty phase in January.