Fort Lauderdale (United States) (AFP) - Nikolas Cruz, who shot and killed 17 people at a Florida high school on Valentine's Day in 2018, planned and carried out a "systematic massacre," a prosecutor arguing for the death penalty said Tuesday.

"What he wanted to do, what his plan was, and what he did, was to murder children at school and their caretakers," assistant state attorney Michael Satz said in closing arguments at the sentencing trial of the 24-year-old Cruz.

"It was calculated. It was purposeful. And it was a systematic massacre," Satz said.

"And he picked Valentine's Day to do it," he told a hushed courtroom packed with family members of those gunned down at Marjory Stoneman Douglas High School in Parkland, a town north of Miami.

Satz recounted the day of the massacre in harrowing detail as Cruz stared down at the table in front of him with his head in his hand.

The 80-year-old Satz, who came out of retirement to try the case, ended his closing arguments by reciting the names of the 17 people who died.

"The appropriate sentence for Nikolas Cruz is the death penalty," he said.

Cruz pleaded guilty to the shooting and it is up to the jury to decide whether he receives the death penalty or life in prison.

If the jury of seven men and five women does not vote unanimously for capital punishment, Cruz will be sentenced to life in prison with no possibility of parole.

The jury is to begin deliberations on Wednesday and will be sequestered until they reach a decision.

'Doomed from the womb'

Melisa McNeill, a lawyer for Cruz, urged the jurors to show compassion for a troubled young man who was born with fetal alcohol stress disorder and put up for adoption by a mother who was homeless, alcoholic and drug-addicted.

"He was doomed from the womb and in a civilized, humane society, do we kill brain-damaged, mentally ill, broken people?" McNeill asked. "Do we? I hope not."

"The state of Florida wants to put you in a place of hate and anger and vengeance," she said.

Quoting the late South African bishop Desmond Tutu, McNeill said: "To take a life when a life has been lost is revenge, not justice."

"This is your individual moral decision," she added.

On February 14, 2018, the then 19-year-old Cruz walked into school carrying a high-powered AR-15 rifle. He had been expelled a year earlier for disciplinary reasons.

In a matter of nine minutes, he killed 14 students and three staff members, then fled by mixing in with people frantically escaping the gory scene.

Police arrested Cruz shortly thereafter as he walked along the street.

The shooting stunned the nation and reignited debate on gun control since Cruz had legally purchased the gun he used despite his history of mental issues.

On March 24, 2018, nationwide marches inspired by school shooting survivors and parents of victims brought together 1.5 million people -- the largest public turnout ever in defense of stricter gun control laws in America.

But the Parkland shooting prompted no significant reform and gun sales have continued to rise.

There have been more mass shootings, including one in May that left 19 young children and two adults dead at an elementary school in Uvalde, Texas.

After the latest shootings, Congress did pass legislation to increase funding for school security and mental health care.