FORT LAUDERDALE, Fla. (AP) — Four years, five months and four days after Nikolas Cruz murdered 17 at Parkland’s Marjory Stoneman Douglas High School, his trial for the deadliest U.S. mass shooting to reach a jury begins Monday with opening statements.

Delayed by the COVID-19 pandemic and legal wrangling, the penalty-only trial is expected to last four months with the seven-man, five-woman jury being exposed to horrific evidence throughout. The jurors will then decide whether Cruz, 23, is sentenced to death or life without the possibility of parole.

“Finally,” said Lori Alhadeff, who wants Cruz executed for murdering her 14-year-old daughter Alyssa. “I hope for swift action to hold him responsible.”

All of the victims’ parents and family members who have spoken publicly have said directly or indirectly they want Cruz sentenced to death.

The former Stoneman Douglas student pleaded guilty in October to the Feb. 14, 2018, massacre and is only challenging his sentence. Nine other U.S. gunmen who fatally shot at least 17 people died during or immediately after their attacks by suicide or police gunfire. Cruz was captured after he fled the school.

Lead prosecutor Mike Satz will give his side’s presentation. Satz, 80, spent 44 years as Broward County’s state attorney and appointed himself lead prosecutor shortly after the shootings that killed 14 students and three staff members. He did not seek a 12th term and left office in early 2021, but his successor, Harold Pryor, kept him on the case.

Craig Trocino, a University of Miami law professor, said Satz will likely emphasize the shooting’s brutality and the story of each victim lost. The prosecution’s theme throughout the trial will be, “If any case deserves a death sentence, this is it,” he said.

“They are going to want to talk about how horrible the crime was, how culpable Mr. Cruz is,” said Trocino, who worked on defendants’ death penalty appeals before joining the law school.

Cruz’s lead public defender, Melisa McNeill, said in court recently that she hasn’t decided whether her team will give its opening statement immediately after Satz or wait several weeks until it’s time to present their case.

Trocino said delaying their opening statement would be a risky and extremely rare defense strategy as it would allow the prosecution to have the only say for half the trial.

He said Cruz’s attorneys will likely want to plant the seed in jurors’ minds that he is a young adult with lifelong emotional and psychological problems. The goal would be to temper the jurors’ emotions as the prosecution presents grisly videos and photos of the shootings and their aftermath, the painful testimony of the surviving wounded and tearful statements from victims’ family members.

The jurors will also tour the sealed-off three-story classroom building where the massacre occurred. It remains blood-stained and bullet-pocked, with deflated Valentine’s Day balloons and dead flowers strewn about.

“The defense will want to put a human face on Cruz,” Trocino said. “They will want to show why life without the possibility of parole is a sufficient punishment.”

During the trial, the prosecution is expected to present an overarching narrative of Cruz’s history of threats, his planning and the merciless nature of the shootings. But they will also spend time on each individual slaying as the jurors will eventually vote on 17 potential death sentences, one for each victim.

Satz’s team will be required to prove beyond a reasonable doubt that Cruz committed at least one aggravating circumstance specified under Florida law, but that should not be an issue. These include murders that were especially heinous or cruel; committed in a cold, calculated and premeditated manner; or committed during an act that created a great risk of death to many persons.

Cruz’s team can raise several mitigating factors that are also in the law. Before the shooting, Cruz had no criminal history. The attorneys can argue he was under extreme mental or emotional disturbance, and his capacity to appreciate his conduct’s criminality or conform it to the law was substantially impaired.

They will likely present evidence that:

— Cruz’s birth mother abused alcohol and drugs during pregnancy. His attorneys say that damaged his brain and left him intellectually disabled, with behavioral problems starting in preschool.

— A “trusted peer” sexually abused him.

— When Cruz was 5, his adopted father died of a heart attack in front of him, which left his adoptive mother to raise him and his brother alone.

— His adoptive mother abused alcohol and died less than four months before the massacre.

— He was an immature 19 when the shootings happened.

For each death sentence, the jury must be unanimous or the sentence for that victim is life. The jurors are told that to vote for death, the prosecution’s aggravating circumstances for that victim must, in their judgement, “outweigh” the defense’s mitigators. A juror can also vote for life out of mercy for Cruz. During jury selection, the panelists said under oath that they are capable of voting for either sentence.

It is possible Cruz could get death for some victims and life for others, particularly since he walked back to some wounded victims and killed them with a second volley. That might swing any hesitant jurors on those counts.

“The prosecution only needs for the jury to come back (for death) on one,” Trocino said.