An unidentified person close to Nikolas Cruz, the teen accused of killing 17 people in a school shooting in Parkland, Florida, called the FBI more than a month before the shooting and said she was worried Cruz would "get into a school and just shoot the place up," a U.S. official familiar with a transcript of the call confirmed to CBS News.

The Wall Street Journal first reported the context of the call made to the agency's public access line. A person familiar with the matter confirmed all of the quotes in the transcript reported by the Journal.

"You know, it's just so much," the caller said. "I know he's -- he's going to explode." The woman said she wanted to clear her conscience in case "he takes off and, and just starts shooting places up."

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"Something is gonna happen," she continued. "Because he's, he doesn't have the mental capacity. He can't, he's so outraged if someone talks to him about certain things."

Last week, the FBI said it had received a tip about Cruz on Jan. 5, 2018, but failed to investigate the report. The caller also reported Cruz's gun ownership, his desire to kill others, erratic behavior and disturbing social media posts. She described times when Cruz mutilated frogs and at least one bird.

"He brought the bird into the house," she said. "He threw it on his mother's kitchen counter and he started cutting it up. He has all kinds of hunting knives. I don't know what knife he used, though. And he started cutting the bird up, and his mother… said, 'What're you doing?' And he says, 'I want to see what's inside.'"

The caller also provided Cruz's social media accounts to the FBI. She said it was alarming to see images on the account and "to know what he's capable of doing and what could happen."

"He's [been] 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."

CBS News correspondent Manuel Bojorquez reports that it wasn't the first time someone called authorities on Cruz. The woman who took in Cruz and his brother after their mother's death last year called Palm Beach County's 911 in November.

"He put the gun at the head of his brother so it's not the first time and he did that with his mom. It's not the first time he put a gun to somebody's head," the 911 caller said.

There are now investigations at practically every level of law enforcement about potential missed warning signs before the shooting and what happened during.

At a Senate Judiciary Committee briefing on Friday, FBI officials discussed how it handled a threat Cruz allegedly made in a post on YouTube on Sept. 15, 2017. The FBI did not seek information from YouTube's parent company, Google Inc., to learn about the identity of the person behind the comment or the individual's location, Sen. Chuck Grassley's office said in a statement. It said Google could have provided information if the agency had asked.

Cruz has been charged on 17 counts of premeditated murder after being questioned by state and federal authorities. His lawyers have said Cruz will plead guilty if prosecutors agree not to pursue the death penalty, but no decision has been made on that.