By Shimon Prokupecz, CNN

(CNN) -- The FBI failed to act on a tip about Nikolas Cruz, the confessed shooter in the Parkland, Florida, school massacre, the bureau said in a statement on Friday.

A person close to Cruz contacted the FBI on January 5 to report concerns about him, the FBI said. But the bureau did not appropriately follow established protocols in following up on the tip.

"The information was not provided to the Miami Field Office, and no further investigation was conducted at that time," the statement said.

The stunning admission is sure to raise further questions about whether the FBI could have prevented the shooting at Marjory Stoneman Douglas High School, which left 17 dead.

The FBI said the caller provided information about "Cruz's gun ownership, desire to kill people, erratic behavior, and disturbing social media posts, as well as the potential of him conducting a school shooting." The information should have been assessed as a "potential threat to life," the bureau said.

FBI Director Christopher Wray said the bureau is still investigating what happened.

"We have spoken with victims and families, and deeply regret the additional pain this causes all those affected by this horrific tragedy," Wray said in the statement. "All of the men and women of the FBI are dedicated to keeping the American people safe, and are relentlessly committed to improving all that we do and how we do it."

Disturbing signs

Cruz has confessed to police to being the gunman, according to a probable cause affidavit. His public defender described him as a "deeply disturbed, emotionally broken" young man who is coming to grips with the pain he has caused.

But as details about Cruz have emerged, so have indications that signs were missed in the months leading up to Wednesday's rampage.

On Thursday, it was revealed that the FBI also was warned in September about a possible school shooting threat from a YouTube user with the same name as Cruz, according to a video blogger.

Ben Bennight, the 36-year-old YouTube video blogger from Mississippi, noticed in September an alarming comment on a video he'd posted. He told CNN he immediately contacted the FBI.

"Im going to be a professional school shooter," read the comment, left by a user with the name Nikolas Cruz.

And documents obtained by CNN show that law enforcement officers responded to Cruz's house on 39 occasions over a seven-year period. No police reports were immediately available for those calls so it was not possible to determine whether Cruz was involved.

Meanwhile, Cruz's digital footprint offers other disturbing glimpses into his mind.

He hurled slurs at blacks and Muslims, and according to the Anti-Defamation League, had ties to white supremacists. He said he would shoot people with his AR-15 and singled out police and anti-fascist protesters as deserving of his vengeance.

This story is breaking and will be updated.

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