"I've spent about four days of hell because my phone won't stop ringing," he said about his contact with investigators.
The man, whose voice was disguised and appeared in a video interview with what appeared to be a mask and makeup, also said Mateen was attracted to Latinos but disliked Puerto Ricans.
At some point afterward, Mateen made the two-hour drive from his home in Fort Pierce to Orlando.
According to CNN, Mateen's wife, Noor Salman, told investigators he left home angry and with a bag of guns.
The Orlando gunman's failed attempt at becoming a correctional officer at Florida jails and prisons was detailed in a series of documents released Friday by the Florida Department of Corrections.
The records show Mateen wanted to be a correctional officer in 2007, but he was written several times for falling asleep in class.
In one incident, the young recruit dozed off at the gun range, while he and his team waited their turn.
In another incident, Mateen was written up for leaving the campus and not telling any of his superiors.
Investigators believe Mateen may have been checking security before the attack, according to CNN.The Department of Justice and FBI on Monday afternoon reversed their decision to release a censored transcript of the 911 call Mateen made from Pulse nightclub, and instead released the full transcript."Unfortunately, the unreleased transcript that named the terrorist organizations and leaders have caused an unnecessary distraction from the hard work that the FBI and our law enforcement partners have already been doing to investigate this heinous crime," a DOJ spokesperson said.Here is the uncensored transcript: Orlando Dispatcher (OD): Emergency 911, this is being recorded. (Special Weapons & Tactics) initiated a full call-out.Omar Mateen (OM): In the name of God the Merciful, the beneficial [in Arabic] OD: What? [End of call.] The FBI on Monday released partial transcripts of telephone calls Orlando nightclub shooter Omar Mateen made during his rampage on June 12. a.m.: Shooter contacted a 911 operator from inside Pulse.