Video has emerged of the suspected Florida gunman practising his shooting in his backyard whilst wearing a 'Make America Great Again' hat.
Nikolas Cruz has been charged with 17 counts of murder after gunning down students and staff at Marjory Stoneman Douglas High School in Parkland, Florida on Valentine's Day.
In video shot by his neighbour in October and obtained by CNN, Cruz can be seen wearing nothing but socks, shorts and a Donald Trump campaign 'Make America Great Again' hat as he fires what appears to be a BB gun in his backyard.
Mr Trump, who counts the powerful pro-gun National Rifle Association amongst his backers, has said mental health is behind the United States' mass shooting epidemic, not lax rules around gun ownership.
FBI admits failures
The FBI says its agents failed to investigate after receiving a tip last month that Cruz had a "desire to kill", access to guns and could be plotting an attack.
Florida Governor Rick Scott has called for the FBI's director to resign because of the missteps.
Attorney General Jeff Sessions says the shooting that killed 17 people on Wednesday was a "tragic consequence" of the FBI's failure and ordered a review of the Justice Department's processes.
Mr Sessions says it's now clear that the nation's premier law enforcement agency missed warning signs.
Dozens of calls about Cruz' behaviour
In more evidence that there had been signs of trouble with the suspect, Broward County Sheriff Scott Israel said at a Friday news conference that his office had received more than 20 calls about Nikolas Cruz in the past few years.
A person close to Cruz called the FBI's tip line on January 5 and provided information about Cruz's weapons and his erratic behaviour, including his disturbing social media posts. The caller was concerned that Cruz could attack a school.
In a statement, the agency acknowledged that the tip should have been shared with the FBI's Miami office and investigated, but it was not.
The startling admission came as the agency was already facing criticism for its treatment of a tip about a YouTube comment posted last year.
The comment posted by a "Nikolas Cruz" said, "Im going to be a professional school shooter." The FBI investigated the remark but did not determine who made it.
The 19-year-old has been charged with killing 17 people at Marjory Stoneman Douglas High School in Parkland, north of Miami.
FBI director Christopher Wray says the agency, which received an average of 2,101 calls to the tip line each day in 2017, is still reviewing its missteps on the January tip.
Mr Wray says he is "committed to getting to the bottom of what happened," as well as assessing the way the FBI responds to information from the public.
Florida's governor sharply criticised the federal law enforcement agency on Friday, calling the FBI's failure to take action "unacceptable".
"Seventeen innocent people are dead and acknowledging a mistake isn't going to cut it," Mr Scott said.
"... The families will spend a lifetime wondering how this could happen, and an apology will never give them the answers they desperately need."
The FBI also is under intense scrutiny for its actions in the early stages of the investigation into Russian meddling in the 2016 presidential campaign.
Reuters / Newshub.