Nikolas Cruz, 23, pleaded guilty to murder and the jury must decide whether to sentence him to death or life in prison without the possibility of parole.

Dressed in a big sweater, large glasses and his face covered by an anti-Covid mask, he appeared on Monday in a court in Fort Lauderdale, where several relatives of his victims had taken their seats.

Some let tears flow when the prosecutor carefully rolled out his murderous trip on February 14, 2018, to Marjory Stoneman Douglas High School in Parkland, from which he had been expelled a year earlier.

“I’m going to tell you the unspeakable,” Mike Satz had warned in his introduction, before recounting how the shooter, armed with a semi-automatic rifle, proceeded methodically through the establishment, firing a total of 139 shots, killing 14 students and three adults.

He then slipped among the fleeing high school students, had a drink in a fast food restaurant, before being recognized by a police officer and arrested.

“The murders were particularly atrocious” but also “cold, calculated, premeditated”, insisted the prosecutor, without mentioning, at this stage, the death penalty.

This trial, which should last several months, has a unique character as it is rare in the United States for the perpetrators of such carnage to survive their attack.

It intervenes in a country reeling from a series of bloody shootings in a primary school (21 dead including 19 children), a supermarket (10 dead, all African-Americans) and a National Day parade (7 dead).

On the first day of the hearing, the court was immediately plunged into the horror of the drama: a video recorded by a student was shown to the jurors, only the sound – screams, groans, tears interspersed with gunshots — being audible to the rest of the audience.

Nikolas Cruz, then covered his face with his hands and bent over to his table.

His lawyers should plead that their client, with a difficult childhood, is mentally ill and recall that he has apologized. “I’m really sorry for what I did, I bear the brunt of it every day,” he said in October.

The prosecution will insist on the premeditated nature of the crime, relying on a video recorded before the act. “Let my massacre begin today. Let all the frightened children run to hide,” he said.

“My life is nothing and has no meaning,” he added, announcing that he wanted to go to his old school in an Uber vehicle, armed with an AR-15 rifle.

Despite his psychiatric history and reports of his dangerousness, Nikolas Cruz had indeed been able to legally buy this rifle, a civilian version of assault rifles.

The Parkland attack was the worst school massacre in the United States since the Sandy Hook school shooting in Newtown, Connecticut, in 2012 in which 26 people were killed.

It had sparked a record mobilization led by several young survivors and the parents of victims. On March 24, 2018, the “March for Our Lives” brought together 1.5 million people across the country, the largest national demonstration for better control of firearms in the history of the United States.

Despite the protesters’ hopes, no legislative reform had been passed in Congress, and gun sales have continued to increase in recent years in the United States, especially during the Covid-19 pandemic.

They have killed more than 24,000 people, including 13,000 suicides, since the beginning of the year, according to the Gun Violence Archives website.

The recent dramas have been followed by the adoption of a modest federal law, which mainly plans to strengthen the funds allocated to school safety and mental health.