PARKLAND, Fla. – A tipster close to Nikolas Cruz told the FBI that the Parkland school shooter was "going to explode," according to a transcript of the Jan. 5 call, made more than a month before the shooting.

"It's so much and I know he's -- he's going to explode," the woman said.

The five-page transcript of the call, first obtained by ABC News, detailed what had been reported to the FBI about Cruz before he killed 17 people at his former school on Valentine's Day. The FBI has admitted to failing to follow up on the tip called in to the FBI's call center in January and sharing it with the bureau's Miami field office.

The tipster also provided details about Cruz’s concerning social media activity, identifying four Instagram accounts and troubling posts, and sharing details about his upbringing, foster family and concerning behavior.

"I just want someone to know about this so they can look into it," the tipster said. "If they think it's something worth going into, fine. If not, um, I just know I have a clear conscience if he takes off and, and just starts shooting places up."

On the call, an intake specialist located in West Virginia asked the caller for information about Cruz and whether he had made any threats of violence or "talk about ISIS."

The tipster, whose name is redacted from the transcript but is identified as an "unknown female," said Cruz "expresses different things" on social media "and then he takes it off."

File: FBI Tip About Cruz Transcript

"Just recently, now he has switched it to he wants to kill people" the tipster said. "And then he put that on his Instagram and about two days later, he took it off."

She also said she had previously called police with warnings about Cruz, giving an officer with the local department "all the information I had."

The tipster described Cruz as a violent child who killed animals, posted frequently about firearms and ISIS, and was "thrown out of all these schools because he would pick up a chair and just throw it at somebody, a teacher or a student because he didn't like the way they were talking to him."

"It's alarming to see these pictures and to know what he's capable of doing and what could happen," the tipster told the FBI on the call. "I just think about, you know, getting into a school and just shooting the place up."

The tipster said she believed something was going to happen.

"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 tipster said.

The intake specialist did not say if the agency would be following up with the caller.

Gov. Rick Scott has called for FBI Director Christopher Wray to resign over his agency's "failure to take action."

Cruz confessed to killing 14 students and three teachers with an AR-15 rifle at Marjory Stoneman Douglas High School. He is being held without bond on 17 counts of premeditated murder.