Florida school shooter Nikolas Cruz told a prosecution psychiatrist he began contemplating a mass murder during middle school, doing extensive research on earlier killers to learn their methods and mistakes to shape his own plans, video played at his penalty trial showed Monday.

Cruz told Dr. Charles Scott during a March jailhouse interview that five years before he murdered 17 at Parkland's Marjory Stoneman Douglas High School on Feb. 14, 2018, he read about the 1999 murder of 13 at Colorado's Columbine High School, which sparked the idea of his own mass killing. Cruz told Scott how Columbine, the 2007 murder of 32 at Virginia Tech University and the 2012 killing of 12 at a Colorado movie theater all played a part in his preparation.

"I studied mass murderers and how they did it," Cruz told Scott. "How they planned, what they got and what they used." He learned to watch for people coming around corners to stop him, to keep some distance from people as he fired, to attack "as fast as possible" and, in the earlier attacks, "the police didn't do anything."

"I should have the opportunity to shoot people for about 20 minutes," Cruz said.

Cruz, 24, pleaded guilty a year ago to the murders that happened during a seven-minute attack on Feb. 14, 2018 — the trial will only decide whether he is sentenced to death or life without the possibility of parole. A unanimous vote by the seven-man, five-woman jury is required for Cruz to get death. Anything less and his sentence will be life.

Prosecutor Mike Satz hopes Scott's testimony will rebut the defense's contention that heavy drinking by Cruz's birth mother during pregnancy caused fetal alcohol spectrum disorder, putting him on a lifelong path of bizarre and sometimes violent behaviorthat culminated in the shootings. The defense also tried to show that his adoptive mother, Lynda Cruz, became overwhelmed after her husband died when Cruz was 5 and never got him complete treatment for his mental health issues. She died less than three months before the shootings.

Scott, a University of California, Davis, forensic psychiatrist, testified Monday that his examinations of Cruz and his school and mental health records don't support the defense findings. He diagnosed Cruz with antisocial personality disorder, saying the 24-year-old former Stoneman Douglas student can control his behavior but chooses not to because he has no regard for others. For example, Scott pointed to Cruz's 14-month employment as a cashier at a discount store with no incidents.

He also said Cruz did well in alternative education classes taken after he was expelled from Stoneman Douglas a year before the shootings, getting a perfect score in a course on violence and guns.

He said Cruz's behavior spiraled after a girlfriend broke up with him 18 months before the killings.

Cruz told Scott that the night before the shootings, he adjusted the sights on his AR-15-style semiautomatic rifle to assure he fired accurately. He imagined how the recoil would feel and how his victims would react. He put on the burgundy polo shirt he received when he was a member of the Stoneman Douglas Junior Reserve Officer Training Corps so he could blend in with students when he fled.

"I couldn't sleep," Cruz told Scott.

Satz also replayed videos Cruz made in the weeks before the shooting where he talked about how he would carry out the killings and hoped for a death toll of at least 20.

Scott said Cruz told him that he chose Valentine's Day for his massacre because "he has no one to love and love him."

"This was not a spur of the moment decision. This was planned out for months," Scott said.

Cruz told Scott he stopped shooting and fled when "I didn't have anyone else to kill."

Circuit Judge Elizabeth Scherer rejected defense attorney Tamara Curtis' attempt to cross-examine Scott about how Stoneman Douglas' guards spotted Cruz as he entered campus carrying a large case just before the shooting, knew he was dangerous and did not stop him or warn teachers to lock their classrooms. Scherer also rejected questions about how Cruz was reported to the FBI and Broward County sheriff's deputies as a potential school shooter, but nothing was done.

"These are all things that should have stopped it. It wasn't that sophisticated (of a crime). They are arguing this was a sophisticated crime," Curtis said. "It is only through a series of unfortunate omissions it was carried off."

Judge Scherer said such questioning would violate Florida's prohibition against blaming crimes on third-party actions. The FBI and Broward County school district did pay a combined $150 million to victims' families and wounded survivors to settle lawsuits accusing them of negligence.

Curtis under cross-examination did get Scott to concede that Cruz generally got failing or low grades throughout school, usually did poorly on standardized tests and made numerous internet searches for suicide methods. He also agreed that Cruz was twice recommended for psychiatric commitment, but that never happened.

The trial, which began July 18, has progressed slowly — Monday was only the second court session in almost three weeks. Because of Hurricane Ian, the trial met just one day last week. That came after a nearly two-week pause following the defense's surprise resting of its case Sept. 14 after calling only about 25 of the 80 witnesses the attorneys had said would testify. The prosecution then needed time to prepare its rebuttal case and schedule witnesses.

That case is expected to conclude this week. Closing arguments would then be given next Monday, followed by deliberations.

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