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TOPSHOT - Marjory Stoneman Douglas High School staff, teachers and students return to school greeted by police and well wishers in Parkland, Florida on February 28, 2018. 
Students grieving for slain classmates prepared for an emotional return Wednesday to their Florida high school, where a mass shooting shocked the nation and led teen survivors to spur a growing movement to tighten America's gun laws. The community of Parkland, Florida, where residents were plunged into tragedy two weeks ago, steeled itself for the resumption of classes at Marjory Stoneman Douglas High School, where nearby flower-draped memorials and 17 white crosses pay tribute to the 14 students and three staff members who were murdered by a former student.
 / AFP PHOTO / RHONA WISE        (Photo credit should read RHONA WISE/AFP/Getty Images)
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TOPSHOT - Marjory Stoneman Douglas High School staff, teachers and students return to school greeted by police and well wishers in Parkland, Florida on February 28, 2018. Students grieving for slain classmates prepared for an emotional return Wednesday to their Florida high school, where a mass shooting shocked the nation and led teen survivors to spur a growing movement to tighten America's gun laws. The community of Parkland, Florida, where residents were plunged into tragedy two weeks ago, steeled itself for the resumption of classes at Marjory Stoneman Douglas High School, where nearby flower-draped memorials and 17 white crosses pay tribute to the 14 students and three staff members who were murdered by a former student. / AFP PHOTO / RHONA WISE (Photo credit should read RHONA WISE/AFP/Getty Images)
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This image made available by the Broward County Sheriff's Office on Sunday, Feb. 18, 2018, shows Sheriff Scott Israel, holding the hand of Anthony Borges, 15, a student at Marjory Stoneman Douglas High School. The teenager was shot five times during the massacre on Valentine's Day that killed 17 students. Borges is being credited with saving the lives of at least 20 other students. (Broward County Sheriff's Office via AP)
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This image made available by the Broward County Sheriff's Office on Sunday, Feb. 18, 2018, shows Sheriff Scott Israel, holding the hand of Anthony Borges, 15, a student at Marjory Stoneman Douglas High School. The teenager was shot five times during the massacre on Valentine's Day that killed 17 students. Borges is being credited with saving the lives of at least 20 other students. (Broward County Sheriff's Office via AP)
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(CNN) —  

More than 30 people knew about confessed Parkland gunman Nikolas Cruz’s troubling behavior, but didn’t report it until after he killed 17 students and teachers at his former school, investigators found.

Several people knew of Cruz’s threats of violence, tendency to mutilate animals and expressed desire to commit a school shooting, an investigator told the Marjory Stoneman Douglas Public Safety Commission during a hearing on Tuesday in Sunrise, Florida. They also knew he had knives and firearms, the investigator said.

“Over a really extended period of time, a lot of people saw Cruz’s behavior – very troubling behavior,” said commission chair, Pinellas County Sheriff Bob Gualtieri. “And in many cases, that probably should have caused them to report what they saw, heard or learned, but for a variety of reasons they did not.”

“The phrase, ‘See Something, Say Something,’ it means something, and it has to be more than a phrase,” the sheriff said.

Cruz, 20, was arrested shortly after the shooting on February 14 and has confessed to being the gunman, court documents show. He is awaiting trial on 17 counts of premeditated murder and 17 counts of attempted murder. Prosecutors have said they plan to seek the death penalty.

A judge entered a plea of not guilty on Cruz’s behalf when he was arraigned in March after his attorney told the judge the teen was standing mute to the charges, meaning he was declining to enter a plea.

Tuesday’s hearing was held on the same day Cruz allegedly tackled and repeatedly punched a jail guard, then took his stun gun in a fight, according to an arrest report. He now faces additional charges of assault, battery and the use of an electric weapon on the guard in the Broward County Sheriff’s main jail.

Cruz’s attorney has described him as a “deeply disturbed, emotionally broken” young man, who suffers from mental illness and trauma. His defense team has said there is no question he did it, and he’s willing to plead guilty to avoid the death penalty.

The sheriff told the commission that people learned of Cruz’s behavior from his social media posts, personal observations and contact him and his family. In some cases, people did report what they learned, but it was never followed up on, the sheriff said.

Three people knew Cruz had made statements about shooting up a school, Pinellas County Sheriff’s Office Detective Chris Lyons told the commission.

Seven others knew of instances of animal cruelty or killing; 19 knew Cruz had knives, bullets or firearms; eight people had knowledge of his statements of hate towards others and 11 of Cruz’s statements of his desire to hurt or kill people, Lyons said.

“Sometimes Cruz would bring deceased animals to school with their heads removed. And Cruz would show other students, and he was proud of the animals that had been killed,” Lyons said.

One student who once rode the school bus with Cruz recalled “that he made bad jokes about Jewish people, Nazis, and Hitler,” Lyons said during his presentation.

“He would also say things like, ‘I wish all the Jews were dead.’ The student described Cruz as racist toward African-Americans,” Lyons said. “Cruz had previously shown him knives and bullets that he’d brought to school.”

Lyons said some of Cruz’s threats were directed at his adoptive mother. Lynda Cruz died last fall following an illness.

A bank employee knew that “Nikolas had directed Lynda Cruz to kill herself or that he would kill her,” Lyons said.

“Lynda made her promise that if anything happened to her, she would tell them it was Nikolas,” Lyons said.

The hearing also focused on how 911 calls were handled on the day of the shooting.

Calls came into Coral Springs, but they had to be transferred to the Broward County Sheriff’s Office, the lead agency, because Coral Springs didn’t have access to the deputies or the radio channel in the communication center, according to Gualtieri.

“It took 28 seconds for Coral Springs to even transfer it over to BSO, and it took BSO 41 seconds to process it – and that’s 69 seconds. At the 69 second mark, Cruz was already pretty much done with the killing on the first floor, Gualtieri told CNN affiliate WFOR.

Scot Peterson, the former Broward County Sheriff school resource officer criticized for his response to the shooting, and Broward County Sheriff Scott Israel are among those expected to testify on Thursday.

CNN’s Nicole Chavez, Eric Levenson and Tina Burnside contributed to this report.