The Orlando shooter called a local TV news station and declared his allegiance to the Islamic State, according to the News 13 producer who took the call.
That producer, Matthew Gentili, said he received a flurry of viewer calls in the station's newsroom early Sunday as word began to spread that something terrible was happening at Pulse nightclub.
But a call around 2:45 a.m. — 45 minutes into the grisly attack that left 49 clubgoers dead — was different.
"I will never forget the words he said to me," Gentili told a reporter at News 13.
The man on the other line asked if Gentili had heard about the shooting. After he said that he had, the caller cut him off.
"I'm the shooter. It's me. I am the shooter," the man said.
According to Gentili, the caller than began to speak in what he believed was Arabic.
"At the time, I didn't know what he was saying. He was speaking so fast. But it was... he was speaking fluently. Whatever language he was speaking, he knew it."
When Gentili asked him to speak English, the caller told him: "I did it for ISIS. I did it for the Islamic State."
Gentili was interview by the FBI following his shift. He said he heard nothing in the background.
While authorities have not confirmed the call came from the shooter, News 13 said they independently confirmed Mateen was linked to the incoming call number.
According to other reports, Mateen also placed a 911 phone call midway through the attack, and pledged allegiance to the terror group in that call, as well.
Authorities say Mateen first opened fire at the Orlando gay hotspot as patrons were saying their goodbyes at about 2 a.m.
A three-hour hostage situation ensued, during which 49 people were killed and dozens more were wounded. Mateen was killed by police at the end of the standoff.