Now playing
03:31
Tipster warned FBI of Parkland school shooter
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
PHOTO: RHONA WISE/AFP/AFP/Getty Images
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)
Now playing
03:32
Regresan a clase los estudiantes de Parkland en medio de medidas de seguridad reforzadas
PHOTO: NBC's "Today"
Now playing
01:25
Parkland school officer: Shooting haunts me
parkland neighbor Joelle Guarino
PHOTO: CNN
parkland neighbor Joelle Guarino
Now playing
03:07
Neighbor: School gunman was pure evil
PHOTO: pool
Now playing
00:41
Watch Florida shooter make court appearance
florida shooting suspect
PHOTO: instagram
florida shooting suspect
Now playing
01:36
Authorities investigating online postings
This image made available by the Broward County Sheriff
PHOTO: Broward County Sheriff's Office via AP
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)
Now playing
00:45
Last Parkland shooting patient leaves hospital
PHOTO: CNN
Now playing
01:36
Florida high school to reopen after massacre
title: File uploaded by user duration: 00:00:00 site:  author:  published:  intervention: no description:
PHOTO: Chai Center Chabad
title: File uploaded by user duration: 00:00:00 site: author: published: intervention: no description:
Now playing
01:37
Surveillance video shows gunman after shooting
PHOTO: Snapchat/MWCSFL
Now playing
00:39
Video shows students hiding as shots are fired
Now playing
02:11
Student recounts classmates being shot
Nikolas Cruz modeling his body armor.
PHOTO: From Instagram
Nikolas Cruz modeling his body armor.
Now playing
01:16
Private messages reveal Nikolas Cruz's dark side
Additional Embargo:       Additional Source(s):        Date Shot: 2/15/2018      Shipping/Billing Info:            Description:     Projects:     None    Cost Center:     Atlanta National Desk / 20100101        Created By: severc    On: 1518689865    --------------------------------------------------------------------------------
PHOTO: WPBF;
Additional Embargo: Additional Source(s): Date Shot: 2/15/2018 Shipping/Billing Info: Description: Projects: None Cost Center: Atlanta National Desk / 20100101 Created By: severc On: 1518689865 --------------------------------------------------------------------------------
Now playing
01:16
Officer describes moment he arrested shooter
PHOTO: Kaitlin Carbocci
Now playing
02:33
How the horror unfolded via text, social media
florida school shooting mother daughter reunite orig mg_00001827.jpg
PHOTO: WPTV
florida school shooting mother daughter reunite orig mg_00001827.jpg
Now playing
01:02
Mom's tearful reunion after shooting
(CNN) —  

A woman close to the Parkland, Florida, school shooter called an FBI tip line in early January to describe a young man with an arsenal of knives and guns who was “going to explode” and 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 a transcript of the January 5 call reviewed by CNN.

The FBI admitted last week that it had failed to act on the tip. In a statement then, FBI Director Christopher Wray said that “we have spoken with victims and families, and deeply regret the additional pain this causes all those affected by this horrible tragedy.”

Nineteen-year-old Nikolas Cruz killed 17 people when he stormed his former school, Marjory Stoneman Douglas High School, with an AR-15 style gun last week.

In the days since the massacre, people who knew Cruz have described a troubled young man who was often at odds with law enforcement and made violent posts online. The FBI and local police have revealed that they had received several warnings about his behavior.

On Friday, officials from the FBI briefed congressional staff on the tip line processes at lawmakers’ request, including Senate Judiciary Chairman Chuck Grassley of Iowa.

In the briefing, the FBI made it clear that the bureau was conducting a review of the tip line process, according to a Capitol Hill staffer who was there.

The Wall Street Journal was first to report on the contents of the transcript.

In the January call, the woman, who is not identified, told the FBI employee that 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 “because he didn’t like the way they were talking to him.”

The woman also provided the FBI employee with the usernames for at least three of Cruz’s Instagram accounts, where he wrote that “he wants to kill people” and posted photos of animals that he had mutilated.

“You know how a bird will fly around in the backyard and then hit your glass door, your sliding glass doors and hit the ground?” the woman said, “Well that’s what happened. He brought the bird into the house. He threw it on his mother’s kitchen counter and he started cutting it up.”

“That to me would be a red flag,” the woman said.

Cruz used money from his mother’s bank account to buy several rifles and ammunition, including one gun that he bought online, the caller said.

After receiving the call, the FBI employee, based in the bureau’s West Virginia tip line center, discussed the tip with her supervisor and the two concluded there was no imminent threat and decided to take no further action, the staffer said. The case was closed within an hour.

During the call, the FBI employee had asked the woman whether Cruz said he was going to take action or that he just wanted to. Replying, the woman read the post where Cruz said, “I want to kill people,” according to the transcript.

At one point in the briefing Friday, the FBI said it may not have been able to take law enforcement action based on the tip because of the shooter’s stated intent and conflicting access to the case with local jurisdictions, according to the Hill staffer.

The FBI also described on Friday a tip it had received through an online portal in September after Cruz made a threatening post on a YouTube video, according to a news release from Grassley’s office.

As a result of that tip, the FBI opened a counterterrorism lead, but the bureau closed it the next month because the FBI could not positively identify the individual behind the post, the statement says.

“The FBI has dispatched officials to both field offices where the tips were received to investigate what went wrong and determine how processes can be improved to prevent future failures,” the statement says.

YouTube’s parent company, Google, also briefed congressional staff Friday and said the comment by Cruz in September was marked as spam and removed by the video’s owner shortly after it was posted and therefore not investigated further, the statement says.

In the briefing, Google “acknowledged that it has a role to play in reviewing its social media sites for content that merits a referral to law enforcement,” the statement from Grassley’s office says.