The FBI says it's investigating whether or not a disturbing YouTube comment reported to them in September was posted by the suspect in Wednesday's deadly Florida school shooting rampage.

A Mississippi man tells CBS News' Jeff Pegues that he warned the FBI last September about a social media comment allegedly posted by Florida school shooting suspect Nikolas Cruz. Ben Bennight says he saw a comment on a YouTube video that troubled him and notified the FBI, Pegues reports. The comment on Bennight's YouTube video said, "I'm going to be a professional school shooter," Bennight said.

Police say Cruz opened fire with a semi-automatic weapon at Florida high school Wednesday, killing 17 people, injuring 15 and sending hundreds of students fleeing into the streets.

The FBI said Thursday they investigated the comment but wasn't able to identify the person who posted it.

BuzzFeed News first reported that the YouTube vlogger says he made the warning. 

Bennight, who BuzzFeed reports is a bail bondsman, spoke with the FBI last year for about 20 minutes, and there was no follow-up from the FBI after that initial conversation, Pegues reports.

Bennight told Pegues he spoke with the FBI Wednesday night again for about 20 minutes. They wanted to know if he knew anything more after first reporting the YouTube video last year. He said the same agent/agents he spoke with last year came to his home Wednesday. 

Robert Lasky, special agent in charge of the FBI Miami Division, said Thursday at a press conference that the FBI received information last year about a comment on a YouTube channel that said, "I'm going to be a professional school shooter."

"No other information was included with that comment, which would indicate a time, location or the true identity of the person who made the comment," Lasky said. "The FBI conducted database reviews, checks, but was unable to further identify the person who actually made the comment."

Lasky said investigators are again reviewing the comment but don't know whether Cruz is the person who posted it.

"We're going back, we're scrubbing the information, we're looking at it again, but I'm not willing to say at this time that it was ... the same person," Lasky said.

The development comes just hours after Broward County Sheriff Scott Israel urged people to call law enforcement if they see something online "that is not right." 

"Call up the FBI or the Broward Sheriff," he said. "You could prevent a major tragedy."