In a statement, the Federal Bureau of Investigation said it received a tip last month from "a person close to Nikolas Cruz" reporting concerns about him, specifically saying that he could potentially carry out a school shooting. The caller said this behavior included a "desire to kill people" and "the potential of him conducting a school shooting".
That information should have been forwarded to the FBI's Miami field office for further investigation, but "we have determined that these protocols were not followed", the agency said. But that never happened.
Nikolas Cruz, 19, was wearing a maroon shirt with the logo from the Army Junior Reserve Officer Training Corps program at Marjory Stoneman Douglas High School when he was arrested Wednesday shortly after the shooting.
In September, a MS man reported to the law enforcement agency a disturbing comment left on a YouTube video by a user called "nikolas cruz" which said: "I'm going to be a professional school shooter".
FBI investigators, however, were unable to determine the source of the post. "This is imperative, and we must do better".
Florida Governor Rick Scott said FBI Director Christopher Wray should step down over the agency's mishandling of the tip.
Authorities say Cruz, who was expelled past year for disciplinary reasons, walked into his former school with an AR-15 and opened fire.
The right to bear arms, as guaranteed in the U.S. Constitution, is seen as sacred in many rural communities in America's heartland, whose support was a major factor that pushed Trump into the White House last November.
The FBI said it was notified about a comment on YouTube five months ago from someone with the username "nikolas cruz".
The FBI is the lead investigative agency into the Wednesday shooting.
The FBI has been under fire for months by Republicans displeased with its probe into the Trump campaign's Russian Federation ties.
Congress criticized the bureau for not preventing the 2009 mass shooting at Fort Hood in Texas, in which the gunman was known to the FBI.
Epstein said that as the death toll of 17 people became clear, he knew he had to help in some way.
Mateen had been interviewed three times before the case was closed.
After those incidents, FBI investigators compared themselves to hockey goalies, fielding a relentless barrage of pucks.
He also said they hope to speak to unnamed others who "might enlighten us as to why he did what he did", Israel said, though he emphasized that a day into the investigation, police did not believe Cruz had any accomplices.
Some students and neighbors of Cruz said they observed troubling behavior. "And there's no question of whether this is the most horrific act ever in Broward County - it is", the lawyer said.
Trump said earlier on Friday that he is traveling to Florida to meet with people impacted by the shooting.
The FBI failed to follow up (paywall) on disturbing tips about Florida shooter Nikolas Cruz, in a lapse that could have consequences far beyond this week's lethal school attack. It investigated the comment but did not determine who made it. The bureau was also reviewing what happened after the agents received the information. He also discussed different firearms with the group chat and wrote, "I think I am going to kill people".
Mass killings like the one seen on Wednesday are becoming increasingly common in the United States, highlighting a problem that only seems to be getting worse, experts said.