(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.

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