Cruz has pleaded guilty to the massacre, so all that remains after nearly three months of often disturbing evidence is for the jury to decide on his punishment.
It has been a gut-wrenching experience for relatives of those gunned down at Marjory Stoneman Douglas High School in Parkland, a town north of Miami.
Lawyers defending Cruz, who is now 24, will present their final arguments on Tuesday. Jury deliberations begin the following day.
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.
On February 14, 2018, the then-19-year-old Cruz walked into the school carrying a high-powered AR-15 rifle. He had been expelled from the school a year earlier for disciplinary reasons.
In nine minutes, he killed 14 pupils and three school employees, then fled by mixing in with people frantically escaping the gory scene.
Police arrested Cruz shortly afterwards as he walked along the street.
The next few days in the Fort Lauderdale courtroom will show whether the prosecution, led by Michael Satz, or the defence, under Melisa McNeill, has laid out a more persuasive case.
Ms McNeill, a public defender, centred her strategy on Cruz's traumatic childhood. She argued that he was born with foetal alcohol stress disorder because his mother, who was homeless, drank heavily while pregnant with him. She also used drugs.
"He was poisoned in the womb," Ms McNeill told the court back in August. "His brain was irretrievably broken, through no fault of his own."
Cruz's birth mother gave him up in a brokered private adoption, Ms McNeill said, but his adoptive mother also became an alcoholic, and he grew up in a broken home.
Cruz told the court that a family friend abused him sexually at age nine, and Ms McNeill said his developmental and behavioural problems were never properly addressed.
Given the challenges he faced, she said, life in prison was a more appropriate punishment than execution.
Prosecutors, however, argued that Cruz knew exactly what he was doing when he walked into the school with a semi-automatic rifle and several ammunition clips.
Mr Satz has said Cruz carried out a "cold, calculated, manipulative and deadly" act — one he had announced in a videotape three days earlier.
Mr Satz played a video of the shooting recorded by another student. Screams, cries and moans were punctuated by gunshots as terrified pupils sought cover from bullets blasting through the classroom door.
Several anguished relatives of the victims fled the courtroom as the video was played, while others wept openly and hugged their loved ones.
Mr Satz called former pupils who had witnessed the shooting to testify and organised a trip for the jury to visit the school.
The prosecutor tried to discredit the idea that Cruz suffered from foetal alcohol syndrome. He elicited testimony from a neuropsychologist, Robert Denney, who accused Cruz of faking brain problems by intentionally doing poorly on psychological tests.
Mr Denney argued that the very fact that Cruz acted with premeditation showed that he understands reality and can control his actions.
The shooting stunned the nation and reignited the 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 defence 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 Uvalde, Texas, in May that left 19 young children and two adults dead at an elementary school.
After the latest shootings, the US Congress passed legislation to increase funding for school security and mental health care.