I found one LA Times article so far that references he bragged to coworkers in the spring of 2013 of his family ties al Qaeda and actually said he belonged to Hezbollah and hoped to die as a martyr when the FBI raided his apartment.
His coworkers called the FBI.
The FBI then launched a 10 month investigation into Mateen.
The FBI agents then concluded he [a young man raised by very religious foreign-born muslims and attending a mosque several times a week] didn’t understand the difference between Sunni and Shiite islam and didn’t have ties to either terrorist organization dropped the ball, I mean case.
Note that one of his relatives or inlaws does indeed belong to an Iranian cultural organization.
Note also that the attack in Orlando was 1 month almost to the day if not the day ... after the top Hezbollah leader in Lebanon was killed.
“didn’t understand the difference between Sunni and Shiite islam “
That the FBI actually believed this demonstrates how stupid and brain-dead the FBI is.