The information should have been assessed as a "potential threat to life", but the proper protocols weren't followed and the Miami office was not notified, the agency explained.
It has also come out that the local police department also received several tips about Cruz and his potentially risky behavior.
Cruz faces his next court date on Monday, and is now being held without bail. Scott on Friday sharply criticized the federal law enforcement agency, calling the FBI's failure to take action "unacceptable".
"There is no doubt something should have been done", says Dan Roberts, former head of the FBI's Detroit branch. "The FBI conducted database reviews and other checks, but was unable to further identify the person who posted the comment".
Thousands of angry students, parents, teachers and neighbors of a Florida high school where 17 people were killed demanded Saturday that immediate action be taken on gun-control legislation, insisting they would not relent until their demands were met.
She also criticised adults who knew the killer was mentally ill for not doing more to prevent him from owning a gun, with the United States leader having tweeted the day after the massacre that Cruz had not been flagged to the authorities.
Cruz's attorneys at the Broward County Public Defender's Office could not immediately be reached for comment.
Starlight on Facebook
"The only question is, does he live or does he die?" The caller was concerned Cruz could attack a school.
To the children at the vigil, Guttenberg said, "When you look at us parents like we are insane, like we are trying too hard to protect you, like we are trying too hard to tell you what not to do ... just remember it's because we love you and we never want to go through the tragedy of losing you". From there, a member of law enforcement is responsible for following up in the case to determine if the applicant should be allowed to purchase a gun. "The only one to blame for this killing is the killer himself", he said.
The officer wrote: Nikolas suffers from mental illness.
Sheriff Israel confirmed that Cruz was a former student at the school who was expelled previous year for unknown "disciplinary reasons".
The cell phone video, first obtained by CNN on Thursday and reportedly taken by a neighbour last October, shows the 19-year-old firing off rounds in his yard before securing the weapon in his waistband and walking inside.
At a vigil for the victims, a crowd of more than 1,000 people, consisting largely of students, chanted, "No more guns! No guns under 21". Funerals for at least two victims were also held.
"He's just always been a really insane kid, I heard some people say one day he would have done this", one Parkland student said after the mass shooting.
Trump did not respond when asked if the nation's gun laws needed to be changed, then walked into another room.
He ran to the third floor, where according to a timeline released by the Broward County Sheriff's Office, three minutes passed before he dropped the rifle and backpack, ran back down the stairs and quickly blended in with panicked, fleeing students.