A woman who called the FBI's tip line in January to express concerns about the teenager now accused of killing 17 people at a South Florida high school last week said she was worried that he was "going to explode."

The caller told authorities that she was concerned that Nikolas Cruz, 19, would "get into a school and just shoot the place up," according to The Wall Street Journal, which reviewed a transcript of the Jan. 5 call.

"You know, it’s just so much,” the woman said. "I know he’s — he’s going to explode."

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The woman said she made the call because she wanted to maintain a "clear conscience" if Cruz decided to carry out such an act, the Journal reported.

Cruz is accused of opening fire on Marjory Stoneman Douglas High School in Parkland, near Fort Lauderdale. The attack left 17 people dead and 14 others injured. He has been charged with 17 counts of premeditated murder.

The FBI acknowledged in a statement last week that it had failed to follow its own protocols when it received a tip in January warning of Cruz's gun ownership, erratic behavior and desire to kill. The bureau never investigated the tip further or passed on the information to its Miami field office.

The call, the FBI said, "should have been assessed as a potential threat to life" and handed over to its Miami office.

The FBI's failure to follow its own procedures after receiving the call has been met with sharp backlash from politicians. Florida Gov. Rick Scott, a Republican, has called on FBI Director Christopher Wray to resign.

According to the Journal, the caller said Cruz had the mental capacity of a 12- or 14-year-old. She also recounted how he had expressed on Instagram that he wanted to kill himself. She reported that behavior to the police, but was not sure what had happened in the investigation.

Eventually, Cruz's desire to kill himself shifted to a desire to kill others, the caller said. She provided usernames for some of Cruz's social media accounts, and told the FBI to look into the matter.

Cruz displayed other red flags, the woman said. For example, he would bring frogs into his mother's kitchen and cut them open. On at least one other occasion, he cut open a bird, the caller said, according to the Journal.

Not all of the details relayed on the call have been confirmed.

Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE said last week that he had ordered a review into the FBI's procedures for handling such tips.