Recently released documents by the St Lucie County Sheriff’s Office in Florida revealed, Mateen told his bosses he survived those taunting making fake stories about his connections with terror suspects.
After which the Federal Bureau of Investigation (FBI) also probe his remarks at that time and found him absolutely not a threat, the documents said.
Mateen had killed at least 49 people and wounded 53 more before being shot dead by police in Orlando massacre, the worst mass shooting in modern US history.
He had pledged loyalty to the Islamic State (IS) group during a call to police before the deadly attack on June 12. The group also later termed him as its fighters.
During 2013, FBI agents also had questioned Mateen twice after he made threatening revelations to his co-workers.
He was interrogated again in 2014 about a possible link with Moner Mohammad Abu-Salha, a US national who carried out a suicide bombing in Syria.
However, the investigation found nothing and the case was closed, the FBI said.
He said he had links to the suspects in the Boston Marathon bombing and also to Nidal Hasan, a former US Army major sentenced to death for killing 13 people at Fort Hood in Texas in 2009.
The records showed that Mateen repeatedly complained of being taunted for being a Muslim while working as a security guard at the local courthouse.
He said a co-worker had teased him, saying, “We have to be careful – Omar may send us a bomb and he will get his 72 virgins.”
On another occasion, Mateen said a deputy told him he had pork oil on his fingers and he was going to rub them on Mateen’s shirt since pork is forbidden in Islam.
In a letter to his bosses at G4S, he said, “I love the United States. The boasting, I did it just to satisfy the gang of co-workers who ganged up against me. I’m 1,000% pure American. I’m against these terrorists, any one of them.”