Why wasn't he stopped? Four Florida shooting warning signs which were missed before Nicholas Cruz shot 17 dead

As the US reels from Nikolas Cruz’s killing spree that left 17 students and teachers dead, attention has turned to the failings that contributed to one of America’s deadliest school shootings.

Cruz, 19, has confessed to carrying out the shooting at Marjory Stoneman Douglas High School in Parkland, Florida, on Wednesday afternoon. He has been remanded in custody after being charged with 17 counts of premeditated murder.

The teenager, who was orphaned after his mother died last year, set off the school’s fire alarm to get all the students out and told police that when they began to flee he discarded his AR-15 rifle and a vest so he could blend into the crowd.

In the wake of the tragedy, questions have emerged over claims that there were several failings that allowed Cruz to carry out the atrocity, including reported ties to a white supremacist group, mental health issues, and reports to the FBI that he may have been considering carrying out such an attack.

1) The FBI were tipped off about him

After the shooting, it emerged that the FBI was tipped off last September about a YouTube user with the name Nikolas Cruz who had expressed a desire to become a “professional school shooter”.

YouTuber Ben Bennight said he told the FBI last year about a comment on the site under Cruz’s name.

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Mr Bennight, whose YouTube username is BenTheBondsman, posted a video on Wednesday saying he had spotted the comment on September 24.

He said he took a screenshot, flagged it for YouTube and called an FBI office in Mississippi to report it.

“I knew that I couldn’t just ignore that,” he said.

The report prompted a visit from two agents the following and Mr Bennight said the FBI had called him again on Wednesday within two hours of the shooting, with one agent also interviewing him in person.

“Basically they’re going to have to get with YouTube about where the comment originated, but I think they already know,” he said.

The FBI has disclosed that the agency investigated the 2017 YouTube comment posted after it was informed about it but the bureau “could not further identify the person who made the comment”.

Agent Rob Lasky said the agency did a database review, but could not determine the time or location of the post, or the true identity of the person making the comment.

The FBI has begun an extensive review into how it handled the apparent tip-off.

2) Teachers knew of his troubled past

Both teachers and pupils remembered Cruz – who was expelled from the school last year – as a troubled teen, with some dubbing him volatile and suggesting that his strange behaviour had caused people to distance themselves from him.

Victoria Olvera, 17, said Cruz was expelled last year because he got into a fight with his ex-girlfriend’s new boyfriend. She said he had been abusive to his girlfriend.

Maths teacher Jim Gard told the Miami Herald that Cruz had been identified as a potential threat to fellow students in the past, saying he believed the the school administration had warned teachers that Cruz had made threats against other teenagers.

He said: “We were told last year that he wasn’t allowed on campus with a backpack on him. There were problems with him last year threatening students, and I guess he was asked to leave campus.”

Chad Williams, an 18-year-old at the high school, said Cruz would set off the fire alarm day after day and finally got expelled in the eighth grade.

One Marjory Stoneman Douglas student was reported as saying that Cruz had been kicked out of school “multiple times”.

The unnamed student told TVNZ: “He got kicked out of school last year, he always had guns on him and stuff like that so he was a little bit of a troubled kid, he always had jokes on it like that.

“It was a lot of crazy stuff that he did, just not right for school. He got kicked out of school multiple times for that kind of stuff.”

Confirming that Cruz was expelled for disciplinary reasons, Broward School District Superintendent Robert Runcie said the teen was transferred to another school in the county because of “issues that arose.

But despite apparently concerns by teachers and pupils, there appears to be no suggestion so far that any of them raised those concerns with law enforcement authorities or flagged Cruz as a potential threat.

3) Why didn’t mental health workers flag him up?

According to ABC News, Cruz has claimed to have heard voices in his head telling him to carry out the massacre.

The teenager’s legal team had revealed he suffers from autism and depression as well as other psychological issues and fellow pupils have described worrying outbursts towards both teachers and pupils, while CNN reported that officers were called to Cruz’s family home to reports including “mentally ill person”.

According to The Washington Post, Cruz had actually been receiving treatment for mental health issues but had stopped going to the clinic sometime late last year.

Robert Runcie warned about growing mental health issues in the US, saying: “Mental health issues in this country are growing and it’s certainly something that needs to be addressed in our school system.”

Donald Trump also chose to address the issue of mental health rather than gun laws in his statement about the tragedy.

The US President promised to “tackle the difficult issue of mental health”, saying he wanted America’s children to know: “You are never alone, and you never will be.”

But Melissa Reeves, former president of the National Association of School Psychologists, told Politico that schools and communities have inadequate resources and the country’s mental health system is “broken.”

Gun laws – the shooting has reignited the debate about gun control laws in the US

4) How can a mentally-ill teen buy a firearm?

The shooting has reignited the debate about gun control laws in the US.

Officials confirmed that Cruz bought the AR-15 rifle used in the massacre lawfully in Florida over a year ago.

Federal law allows people 18 and older to legally purchase long guns, including the kind of assault weapon used in the attack.

US federal law stops people who have been committed due to mental illness from buying guns, but the fact that Cruz never had, nor received any court order in connection with mental illness, meant he was able to lawfully buy the gun.

Cruz had apparently taken the gun with him when he moved in with his friend’s family and they allowed him to keep it. The family reportedly made him keep the gun in a locked gun cabinet in the house but Cruz had a key.

The shooting prompted Jimmy Kimmel to criticise Donald Trump for doing “worse than nothing” over gun violence, saying: “Tell your buddies in Congress… all the family men who care so much about their communities, that what we need are laws. Real laws that do everything possible to keep assault rifles out of the hands of people who are going to shoot our kids.”

Kimmel added: “Tell these Congressmen and lobbyists who infest that swamp you said you were going to drain – force these allegedly Christian men and women who stuff their pockets with money from the NRA (National Rifle Association), year after year after year, to do something. Now. Not later.”

While “children are being murdered” the president has “done worse than nothing”, he said, adding that “one of your very first acts as president was to roll back the regulations that were designed to keep firearms out of the hands of the mentally ill”.

Former president Barack Obama called for “common-sense gun safety laws”, tweeting: “We are grieving with Parkland. But we are not powerless. Caring for our kids is our first job.”

He added: “And until we can honestly say that we’re doing enough to keep them safe from harm, including long overdue, common-sense gun safety laws that most Americans want, then we have to change.”

During a vigil for the 17 victims of Cruz’s attack, some mourners wielded signs asking for action to fight school violence, including gun control.

“Kids don’t need guns. No guns under 21,” read one sign.

At one point during the vigil, some in the crowd began shouting, “No more guns! No more guns!”