The Orlando nightclub gunman, 29-year-old US citizen Omar Mateen, who voiced his allegiance to Islamic State, was able to legally purchase an entire arsenal of guns and perpetrate the massacre despite several FBI interrogations over alleged links to terror suspects.

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ISIS-inspired attack

Following the deadly shooting spree in Orlando, Florida, local FBI chief Ron Hopper acknowledged that New York-born US citizen Mateen had professed his Islamic State (IS, formerly ISIS/ISIL) allegiance during a 911 call he made from the nightclub at the time of the attack.

The IS propaganda machine was also quick to claim responsibility for the mass shooting by distributing a message via Amaq News that the atrocity was “carried out by an Islamic State fighter.”

However, the IS claim may be nothing more than a propaganda move to capitalize on a massacre perpetrated by a lone-wolf attacker who could have had no direct links to the terror group, security experts told RT.

The suspect’s former wife described him as abusive and emotionally and mentally unstable, and said that her family had to “rescue” her from her ex-husband during their divorce. Meanwhile his former coworker noted that Omar Mateen frequently “talked about killing people” and made racist and homophobic comments, but the company refused to act because it did not want to be accused of Islamophobia.

Gunman long known to FBI

While confirming that Mateen had not been under active investigation at the time of the deadly Sunday assault, Hopper revealed that the 29-year old, who was brought up by a family of first-generation Afghan immigrants, had been on the FBI’s radar for years.

In 2014, Mateen was interviewed by FBI agents over his alleged contacts with Moner Mohammad Abu-Salha, likely the first ISIS-inspired American suicide bomber in Syria. Mateen had allegedly visited the same Mosque as Abu-Salha, but the federal agents determined that the 29-year-old’s contact with the jihadist was “minimal.” The case was then closed, Hopper said.

A year earlier, the FBI interviewed Mateen twice about “inflammatory comments” the suspect allegedly made to a co-worker about possible ties to international terrorism. Unable to “verify” the comments, the FBI was forced to close the case, Hopper said, adding that in both cases the gunman cooperated with investigators.

Guns purchased legally

Because the suspect had been cleared after being interviewed by the FBI, it allowed him to legally obtain a Glock handgun and an AR-15 rifle. Following the deadly shooting a Bureau of Alcohol Tobacco Firearms and Explosives said that Mateen purchased the guns he used in the assault in Florida within the “last few days.'”

The attacker had worked for the world's largest security services firm G4S since 2007 and carried a gun as part of his duties, the company said, adding that the company has been trying to ascertain whether any guns used in the attack were related to Mateen's work.

Florida law requires a mandatory three-day waiting period for handgun purchases, but no permit, registration or licensing is needed to buy or own rifles, shotguns or handguns. Condemning the horrific attack, US President Barack Obama said that the tragedy is a reminder “of how easy it is for someone to get their hands on” a weapon.

Deadliest mass shooting in US history

With at least 49 killed and 53 injured, the Orlando massacre has become “the most deadly shooting in American history,” according to Obama. The US president called the shooting an “act of terror and an act of hate,” conducted by an individual “filled with hatred.”

Initially police announced that 50 people had been killed, apparently mistakenly counting Mateen as a victim.

READ MORE: Deadliest mass shooting in US history: 50 dead, 53 injured in Orlando gay club massacre

The second deadliest US shooting spree was the Virginia Tech assault of April 2007. An outburst of gunfire at a Virginia Tech dormitory followed two hours later by a string of attacks at a classroom building, killed 32 students, faculty and staff and left 17 others injured.

The Sandy Hook Elementary School massacre closes the top three deadliest US shooting rampages. A total of 26 people, including 20 schoolchildren, were killed at the school on December 14, 2012. The shooter, Adam Lanza, 20, also killed his mother at their home.

Tragedy immediately politicized, reignites gun-control debate

As world leaders, from Washington to Moscow and Vatican, expressed their deepest condolences over the tragic loss of life, US politicians rushed to capitalize on the tragedy for their political aims.

Republican presidential hopeful, Donald Trump initially took to Twitter to say he was “right” about the danger of radical Islam in America: “Appreciate the congrats for being right on radical Islamic terrorism, I don’t want congrats, I want toughness & vigilance. We must be smart!”

“Because our leaders are weak, I said this was going to happen - and it is only going to get worse," Trump said in a longer statement released on Sunday afternoon. “I am trying to save lives and prevent the next terrorist attack.”

“We can’t afford to be politically correct anymore,” added Trump, once again slamming Obama who “disgracefully refused to even say the words Radical Islam.”

Trump’s opponent, Clinton called the shooting “an act of terror” that calls for more efforts to combat terrorism and introducing stricter gun controls.

“For now, we can say for certain that we need to redouble our efforts to defend our country from threats at home and abroad. That means defeating international terror groups, working with allies and partners to go after them wherever they are, countering their attempts to recruit people here and everywhere, and hardening our defenses at home,” Clinton said in a statement on Sunday.

Responding to Trump’s attack, Clinton's communication director Jennifer Palmieri wrote that, the Republic has offered “no real plans to keep our nation safe and no outreach to the Americans targeted, just insults and attacks.”

Democratic presidential hopeful Bernie Sanders stayed out of the political bickering, just saying “our ... hopes go out to all those who were shot that they can recover.”

“Twenty-five years ago, I believed that in this country that we should not be selling automatic weapons which are designed to kill people,” Sanders said on NBC's “Meet the Press” early Sunday. “We have got to do everything that we can on top of that to make sure that guns do not fall into the hands of those who should not have them: criminals, people who are mentally ill. So that struggle continues.”

For his part, the Libertarian party’s presidential nominee Gary Johnson called the Orlando shooting “both cowardly and infuriating” as he warned against politicizing the slaughter: “We must allow the authorities to do their jobs, understand how this attack came about, and then respond accordingly. It is not a time to either politicize or jump to conclusions.”