A woman close to the Florida shooter called the FBI tip line in January with an alarming message: Nikolas Cruz is "going to explode."
"I just want to, you know, get it off my chest in case something does happen," the woman said, according to a transcript of the January 5 call reviewed by CNN.
Nearly six weeks after that call, Cruz gunned down 17 people at his former high school in Florida -- one of the deadliest mass shootings in modern US history.
In the weeks leading up to the February 14 massacre, people reported warning signs about Cruz, 19, but law enforcement officials failed to act. And during the shooting, the deputy assigned to the school stayed outside the building where the carnage happened, authorities said.
Here are other revelations that emerged this week:
Tipster warned the FBI
An unidentified woman close to Cruz called the FBI tip line to describe a young man with an arsenal of knives and guns who was "going to explode." She said she feared him "getting into a school and just shooting the place up."
"I just want to, you know, get it off my chest in case something does happen and I do believe something's going to happen," the woman said, according to the transcript CNN reviewed.
The woman said Cruz had the mental capacity of a 12- to 14-year-old and had been kicked out of school for throwing chairs at students and teachers. She also provided the FBI with the user names for at least three of Cruz's Instagram accounts, where he wrote that "he wants to kill people" and posted photos of mutilated animals.
The FBI admitted last week it had failed to act on that tip.
Separately, the FBI was warned in September about a YouTube commenter named Nikolas Cruz, who wrote: "Im going to be a professional school shooter."
Sources: While bullets flew, deputies waited
When Coral Springs police officers arrived at Marjory Stoneman Douglas High School in Parkland during the shooting, many officers were surprised to find that Broward County Sheriff's Deputy Scot Peterson, the armed school resource officer, along with three other sheriff's deputies, had not entered the building, sources tell CNN. The deputies had their pistols drawn and were behind their vehicles, the sources said. Not one of them had gone into the school.
With direction from the Broward deputies who were outside, Coral Springs police soon entered the building. New Broward County sheriff's deputies arrived on the scene, and two of those deputies and an officer from Sunrise joined the Coral Springs police as they went into the building.
It's unclear whether the shooter was still in the building when they arrived.
Sources cautioned that tapes are under review and official accounts could ultimately differ from recollections of officers on the scene.
Peterson resigned following his suspension Thursday, and an internal investigation is pending.
The Broward Sheriff's Office said it is investigating reports that the three additional deputies didn't attempt to make entry into the school after the shooting started.
In 911 call, a teen in crisis
Weeks after Cruz's mother died in November, he reportedly called 911 to describe a tumultuous encounter with a family that had recently taken him in.
In a call obtained by CNN affiliate WPTV, the caller, identified by the West Palm Beach station as Cruz, talks about a blowup. The man, whose voice is unsteady, says he doesn't know where he is calling from because he is new to the area.
The call was placed shortly after Cruz and his younger brother moved in with the Deschamps family in Palm Beach County.
On November 28, Rocxanne Deschamps, who took them in, called 911 saying that Cruz was distraught and violent after losing a photo of his mother, according to the Palm Beach County deputy's report and dispatcher notes. She told authorities that Cruz was confronted by her son, Rock, and ran from the home, saying he "was going to get his gun and come back," records show.
Cruz placed a 911 call after he left, WPTV reported.
"The thing is, I lost my mother a couple days ago, so, like, I'm dealing with a bunch of things right now," Cruz said, according to the TV station.
Cruz lived with that family briefly, then moved out.
More calls under review
That was not Cruz's only interaction with authorities. The Broward County Sheriff's Office said it received 23 calls related to him or his brother in the past decade.
Two deputies have been placed on restricted duty pending an internal investigation on how they addressed the warnings, Sheriff Scott Israel said. Two calls especially are under review: one from February 5, 2016, and another from November 30.
In the 2016 one, officers received information from a neighbor's son that Cruz planned to "shoot up" an unknown school. There was a picture of a "juvenile with guns" on Instagram, according to police records.
In that case, a deputy responded and determined Cruz had knives and a BB gun. The information was forwarded to a school resource officer, police records show.
In November's incident, a caller warned that Cruz was collecting guns and knives and wanted to join the Army. The caller said Cruz was suicidal and could be a "school shooter in the making," according to police records.
The report said that officers at the time did not write a report on the tip. Cruz was no longer living at the listed Parkland address and lived in Lake Worth, Florida, according to police records. The deputy referred the caller to the Palm Beach County Sheriff's Office.
Both calls are listed as being under internal affairs investigation. The 21 other calls are listed as "no policy violation apparent."
CNN obtained records from the Palm Beach County Sheriff's Office that detailed deputies' interactions with Cruz.
Security footage of shooting wasn't live
In yet another revelation, authorities said Thursday that surveillance footage from the school shooting was not shown live, as responding officers initially thought.
Police were watching it on a 20-minute delay, leading them to believe the gunman was still in the building when he was long gone, according to Coral Springs Police Chief Tony Pustizzi.
"The delay never put us in a situation where any kids' lives were in danger, any teachers' lives were in danger," Pustizzi said at a news conference.
However, at some point, there was a miscommunication, and officers believed they were watching real-time footage, he said.
"Somebody would say, 'He's on the second floor,' and we had guys on the second floor saying, 'We're on the second floor, we don't see him,' " Pustizzi told the Sun Sentinel newspaper.
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