He purchased weapons used in the shooting, which killed 49 people, legally within the last week

The dead Orlando terrorist who murdered at least 49 people at an Orlando nightclub was investigated by the FBI for terror links twice - and was linked to American suicide bomber Moner Abu Salha.

Agents did not charge Omar Mateen on both occasions and concluded he 'only had minimal contact' with Florida man Abu Salha who blew himself up for the Al Nusra Front in Syria 2014.

Mateen was also investigated by the FBI for making 'inflammatory remarks' to his colleagues alleging that he had terrorist ties – but again no further action was taken.

He kept his job with a global security firm, G4S, and was able to legally buy guns that were used in the worst mass shooting in American history that killed 49 and injured 53 others inside the Orlando gay nightclub.

Mateen called 911 to pledge allegiance to ISIS during the massacre and also praised the Boston bombers.

It is also claimed that Mateen had connections with a former U.S. Marine and undercover FBI agent turned radical Muslim cleric who was released from jail last year despite warnings that he was recruiting potential terrorists.

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Pictured: US citizen Omar Mateen, 29, the suspected Islamic extremist who slaughtered at least 49 people inside a gay club in Orlando. The FBI says Mateen was a person of interest both in 2013 and again in 2014

Police were at Mateen's most recently listed address in Port St. Lucie this morning. The FBI believe Mateen, who was shot dead by officers, may have 'leanings to radical Islamic terrorism'

Mateen's father said the attack had 'nothing to do with religion' and said his father became angry when he saw two men kissing in Miami several months ago

Marcus Dwayne Robertson, also known as Abu Taubah, managed to convert 36 people to his poisonous version of Islam during his four years in jail, and was considered so dangerous that he was kept shackled with his own security detail away from other inmates.

Mateen was a member of the Timbuktu Seminary, an educational website run by Robertson that police believe is used to dispense his radical teachings, sources told Fox News.

Robertson and several associates were rounded up for questioning early Sunday, sources added.

After serving as a Marine for six years, Robertson went on to become a bank robber, before turning FBI informant after his arrest in exchange for a short prison sentence.

He was dismissed by the FBI in 2007 after allegedly attacking his CIA handler, and then began preaching Islamic extremism.

Thrown in jail for tax fraud back in 2011, prosecutors attempted to have ten years added to his sentence last year after discovering documents preaching terror among his possessions. However, a judge freed him.

Mateen, from Port St Lucie in Florida, shot more than 100 people, killing 49 and injuring 53 others with an AR-15 assault rifle and handgun on the dance floor at Pulse night club early Sunday morning.

The shooter, who had no criminal history, was licensed to work as an armed security guard in Florida, law enforcement sources said.

Mateen was shot dead in a shootout with police.

Mateen is believed to be a member of Timbuktu Seminary, a website purporting to educate Muslims, but actually used to peddle radical Islam by Marcus Dwayne Robertson, also known as Abu Taubah (left and right)

Robertson was a Marine and bank robber before turning FBI snitch and eventually radical cleric. He was jail for tax fraud in 2011, and had to be kept in solitary in jail because of how many people he converted

An FBI spokesman said at a press conference later in the day that Mateen purchased multiple guns in the past few days.

The spokesman said that the investigations by the FBI were closed and that's why the 29-year-old gunman was able to purchase the weapons.

The federal agency said Mateen was first interviewed in 2013 after he made 'inflammatory remarks' to a colleague.

'The FBI first became aware of Mateen in 2013 as he made inflammatory comments to coworkers, alleging possible terrorist ties,' Ron Hopper an FBI special agent said during a press conference.

'The FBI thoroughly investigated the matter including interviews of witnesses, physical surveillance and records checks.

'In the course of the investigation, Mateen was interviewed twice.

'Ultimately we were unable to verify the substance of his comments, and the investigation was closed.'

In 2014, Mateen came to the FBI's attention again and agents interviewed him about a potential connection he may have had with American suicide bomber Moner Abu Salha, who lived about 30 minutes away in Vero Beach, Florida.

'We determined that contact was minimal and didn't to constitute a substantive relationship or threat at that that time,' Hopper said.

In addition, the Bureau of Alcohol, Tobacco and Firearms said that Mateen purchased two weapons legally within the last week.

'He is not a prohibitive person so he can legally walk into a gun dealership,' the representative from the ATF said. 'He did so within the last week or so.'

Marcus Dwayne Robertson, also known as Abu Taubah, managed to convert 36 people to his poisonous version of Islam

The FBI interviewed Mateen in 2013 and closed the investigation and then opened another in 2014 when he came to the FBI's attention again. Agents interviewed him about a potential connection he may have had with American suicide bomber Moner Abu Salha (pictured above)

Attack: A woman sits on the ground outside the club while another party-goer, whose legs are covered in blood, stands beside her

Response: Emergency services are pictured at the scene outside the Pulse nightclub in Orlando, Florida following Sunday morning's shooting

'He's a known quantity,' another source said. 'He's been on the radar before.'

Global security firm, G4S, confirmed that he worked for the company since 2007.

'We are shocked and saddened by the tragic event that occurred at the Orlando nightclub,' a statement by the company reads.

'We can confirm that Omar Mateen had been employed with G4S since September 10, 2007. We are cooperating fully with all law enforcement authorities, including the FBI, as they conduct their investigation.

'Our thoughts and prayers are with all of the friends, families and people affected by this unspeakable tragedy.'

An FBI spokesman said Sunday's mass shooting is being investigated as an act of terrorism, adding that they are looking into whether it was an act of domestic or international terror, and if the Mateen was a lone wolf.

The FBI believe Mateen may have 'leanings to radical Islamic terrorism'.

But his father, Mir Seddique, told NBC News his son became angry when he saw two men kissing in Miami several months ago.

'This has nothing to do with religion,' he said. 'We are saying we are apologizing for the whole incident. We weren't aware of any action he is taking. We are in shock like the whole country.'

Twitter accounts which claim to be affiliated to the Islamic State have hailed the shooting, although DailyMail.com cannot confirm whether the terror group was behind the attack.

Distraught: A woman sits outside the nightclub following the mass shooting. At least 49 people were killed by the suspected gunman

Demetrice Naulings (left) sobs outside the Orlando Police Headquarters where police are interviewing witnesses. Right: People wait outside the emergency entrance of the Orlando Regional Medical Center hospital after the shooting at Pulse gay club

Mateen, a Muslim and father to a three-year-old son, was born in 1986 in New York and married Sitora Alisherzoda Yusufiy, who was born in Uzbekistan, in 2009.

Mateen's father, Seddique Mateen, told NBC News: 'We were in Downtown Miami, Bayside, people were playing music. And he saw two men kissing each other in front of his wife and kid and he got very angry.

'They were kissing each other and touching each other and he said, 'Look at that. In front of my son they are doing that'. And then we were in the men's bathroom and men were kissing each other.'

Mateen's father, Seddique Mateen, pictured, said: 'We were in Downtown Miami, Bayside, people were playing music. And he saw two men kissing each other in front of his wife and kid and he got very angry'

Seddique said his son attended Indian River State College, as well as having an associates degree in criminal justice.

Manteen had a Statewide Firearms License and was trained in firearms, according to Fox News.

Hopper said Mateen made 'threats in the past that he has ties to terrorist organizations'.

Police were at his apartment in Port St. Lucie this morning. Ken Mascara, Sheriff of Port St. Lucie County, told DailyMail.com: 'We have sealed the apartment where Mateen was living. The FBI is bringing bomb diffusing equipment.'

Police, army and FBI surround the club after a suspected Islamic extremist wielding an assault rifle and a handgun killed 49 people

After spending most of the day searching Mateen’s Port St. Lucie home, cops and the FBI moved on late in the afternoon to the custom-built four-bedroom home a couple of blocks of north on Bayshore Boulevard where his parents live.

Neighbor, Tony Schneider, a retired deputy sheriff told Daily Mail Online that Seddique and Shahla Mateen are ‘the nicest people in the world.’

‘They are very Americanized, he said. ‘Just very good neighbors. I have known them for six years and have never had any problems with them.

‘My heart goes out to them — of course if they were involved they can rot in hell, but I otherwise I feel so sorry for them.’

Schneider said that Seddique — who he knows as Sid — can often be seen in his yard and walking up and down the street. He said he did not know his wife nearly as well.

‘I believe he is in insurance, he has done well for himself and they have three daughters, all went to college, who I believe are in the medical field.

‘But I didn’t know the son. I saw his picture on television this morning and I recognized him, but he only came here rarely.’

Authorities at the home of Seddique, the father of Omar Mateen, who shot dead 49 people in an Orlando nightclub

Mateen exchanged gunfire with an officer working around the club at 2am before going back inside, according to Orlando Police Chief John Minia.

Writing on Facebook, Pulse, which described itself as the most prominent gay club in Orlando, urged party-goers to 'get out and keep running' as bullets started to fly.

There were about 320 people inside the club at the time of the shootings and about 100 people were taken hostage.

At around 5am authorities sent in a SWAT team to rescue the hostages. Nine hero officers used a 'controlled explosion' to distract the shooter before fatally shooting him and were able to rescue about 30 hostages who were hiding in the bathroom of the club.

During the gunfire, an officer was shot, but he was saved by his helmet. It was thought that at least one hostage had been locked in a bathroom with gunshot wounds.

Mayor Buddy Dyer said in a press conference: 'Many were saved by the heroic efforts of the men and women of the OPD, the Orange County Sheriffs, Seminal County Sheriff's office.'

At around 6am local time police tweeted: 'Pulse Shooting: The shooter inside the club is dead.'

Since the news of the horrific shooting emerged, celebrities and politicians are calling for stricter gun control laws.

President Obama furthered his gun control message today when addressing the massacre in Orlando.

'Although it's still early in the investigation we know enough to say that this was an act of terror and an act of hate,' Obama said, making no reference to ISIS or Islamic terror in his brief remarks.

SNAPCHAT AUDIO CAPTURES SCREAMING HORROR AS GUNMAN FIRED 24 SHOTS IN JUST NINE SECONDS A Snapchat video captured the sound of 24 gunshots being fired in just nine seconds at Orlando's Pulse nightclub on Sunday morning. The footage obtained by WESH 2 News shows a dark street with police cars flashing in the distance. In the background, there is the sound of one assault rifle firing two or more shots a second, and a woman's scream. At the end of the video there is the sound of a gunshot from another gun. The person filming says: 'Oh... my god... People are getting shot dude...' A male voice next to him says: 'We need to get out of here.' But they stand there stunned as the gunshots keep going. 'This guy's firing out shots,' the friend adds. The harrowing footage offers a glimpse into the horror that unfolded in Florida between 2am and 5am this morning. Advertisement

Obama called the shooting spree, at the gay nightclub Pulse during Pride month in the United States, a reminder of how easy it is for someone to get a hold of a weapon that could kill people in a 'school, or a house of worship, or a movie theater, or in a nightclub.'

'And we have to decide if that's the kind of country we want to be,' Obama said.

'And to actively do nothing is a decision as well,' the president added.

Both Donald Trump and Hillary Clinton took to Twitter on Sunday morning to give their initial reactions to what's now being called the most deadly shooting in United States history.

'Woke up to hear the devastating news from FL. As we wait for more information, my thoughts are with those affected by this horrific act,' Clinton wrote on Twitter, signing it with her trademark 'H' to show that the message was actually penned by the Democratic candidate.

In a statement made by her campaign later, Clinton also called for gun control.

'This is the deadliest mass shooting in the history of the United States and it reminds us once more that weapons of war have no place on our streets,' Clinton said.

Trump made Twitter followers aware of the shooting, then went back to attacking Clinton – this time for a new general election ad – before penning another tweet about the tragedy in Orlando, in which a gunman entered a gay nightclub and mowed down 49 people, with another 53 left injured.

'Appreciate the congrats for being right on radical Islamic terrorism, I don't want congrats, I want toughness & vigilance. We must be smart!' Trump later wrote.

Celebrities have also taken to Twitter to send their support to the LGBT community and demand change to gun laws.

President Obama only spoke for a handful of minutes, but reminded the country of his position on gun control, though didn't bring up 'radical Islamic terror,' the line Republicans use to define the ISIS crisis

John Legend and Josh Groban both wondered when anything was going to change in a country where the last horrific massacre, in San Bernadino, California, happened just six months ago.

'Horrified by the mass shooting in Orlando,' Legend tweeted. 'When will we do something to prevent these killing sprees?'

Groban wrote that he was heartbroken for the victims, the LGBT community, and the entire country, while Ellen DeGeneres summed up her emotions with just one word: 'Sobbing.'

'When does it end?' he wrote.

Prominent LGBT figures like Billie Jean King, Melissa Etheridge, Adam Lambert and Dan Savage spoke out after the killing.

Lambert sent prayers to his 'brothers and sisters' who were at Pulse Nightclub, which describes itself as the most prominent gay club in Orlando, during the horrific attack.

'My heart is with Orlando. My sweet brothers and sisters,' rock singer Melissa Etheridge echoed, including the hashtags EndGunViolence and LGBT.