A jury is deciding whether a teenage gunman who shot dead 17 people at a Florida high school will go to prison for life or be executed.
Expelled student Nikolas Cruz was 18 when he legally purchased the AR-15 rifle he used to shoot dead 14 students and three staff members at the Marjory Stoneman Douglas High School on Valentine's Day in 2018.
It is the deadliest shooting to reach trial in US history.
Nine other gunmen who killed at least 17 people died during or immediately after their shootings, either by suicide or police gunfire.
The suspect in the 2019 shooting of 23 people at a Walmart in El Paso, Texas, is awaiting trial.
Three days before the massacre at Marjory Stoneman, Cruz made a video. In it he said: "Hello, my name is Nik. I'm going to be the next school shooter of 2018.
''My goal is at least 20 people.... It's going to be a big event, and when you see me on the news, you'll know who I am.
"You're all going to die. Ah yeah, I can't wait."
Last October Cruz pleaded guilty to premediated murder and this week, the "penalty phase" of his trial begins. Jurors will determine whether he should be sentenced to life in prison or receive the death penalty.
Walmart agrees to restrict gun sales following Parkland shooting
More than 700 people shot dead in the US since the Texas school shooting
In his opening remarks prosecutor Mike Satz highlighted Cruz's brutality as he stalked a three-storey classroom building and fired his AR-15 semi-automatic rifle down hallways and into classrooms.
Cruz, he said, sometimes walked back to already-wounded victims and killed them with a second volley of shots.
Cruz was "cold, calculated, manipulative and deadly," he added.
Families of the victims were at the Broward County Courthouse in Fort Lauderdale, for the hearing. Some shook their heads, some wept.
Cruz was slumped over during much of Mr Satz's statement.
The court was told Cruz had a history of mental health and behavioural problems at the time of the
He had said at the time of his guilty plea he was "very sorry" and asked to be given a chance to help others.
The jury must be unanimous to recommend Cruz be executed. If any of the 12 jurors objects, Cruz will be sentenced to life in prison without parole.
US gun violence has been the focus of renewed worldwide attention following recent mass shootings including one at an Independence Day parade outside Chicago that killed seven people, and another in May at a school in Uvalde, Texas, that left 19 children and two teachers dead.
On Monday, the man accused of killing 10 black people at a New York grocery shop pleaded not guilty to 27 hate crime and firearms charges stemming from the Buffalo shooting massacre, which he live streamed on social media.
In June, President Joe Biden signed the first major federal gun reform in three decades, which he has celebrated as a rare bipartisan agreement.
But individual states are already looking at introducing ways of countering that.