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.
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.
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.'[. . .]
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.'
ISIS killer was linked to American suicide bomber and had been interviewed by the FBI THREE times
WARNING: GRAPHIC CONTENT
The FBI named Orlando gay club shooter Omar Mateen, 29, a person of interest in 2013 and again in 2014
Investigation was first opened in 2013 when he made 'inflammatory remarks' to colleagues alleging possible terrorist ties
FBI interviewed witnesses, looked at physical surveillance and records checks and also interviewed him twice, but closed investigation
Second investigation was opened to see if he had ties to American suicide bomber Moner Abu Salha, but no links were found and case was closed
Sources say Mateen also used website Timbuktu Seminary, run by radical Islamic cleric Marcus Dwayne Robertson, also known as Abu Taubah
He purchased weapons used in the shooting, which killed 49 people, legally within the last week
FBI says Mateen may have 'leanings to radical Islamic terrorism' and it is being investigated as 'an act of terrorism'
Mateen's father claims the attack has 'nothing to do with religion'
He said his son became angry after seeing two men kiss in public
See more of the latest news on the Orlando shooting at Pulse gay club
By MATT HUNTER FOR MAILONLINE and JENNY STANTON and REGINA F. GRAHAM and ANNETA KONSTANTINIDES and JOSE LAMBIET IN FLORIDA and MARTIN GOULD IN PORT ST. LUCIE, FLORIDA and LOUISE BOYLE IN ORLANDO FOR DAILYMAIL.COM
PUBLISHED: 11:47 EST, 12 June 2016 | UPDATED: 09:58 EST, 13 June 2016