11:15 AM PT -- There are now reports Omar Mateen called 911 and pledged his allegiance to ISIS before carrying out the deadly shooting. He also mentioned the Boston Marathon bombing.

ISIS is taking credit for the attack, saying, "a soldier of the Islamic State has carried out the attack."

The killer in the Orlando nightclub slaughter is 29-year-old Omar Mateen. TMZ has done a records search and found he held a Florida security officer license and a state firearms license.

He's an American citizen and he has family that are not -- his parents are Afghan. Authorities say he was a terrorist and was targeting gays. They say in addition to terrorism this is a hate crime.

Authorities also believe he is part of the radical Islam movement, although they do not know if it was an organized attack or if he was a lone wolf. Authorities also believe Mateen specifically targeted a gay club.

Mateen's father told NBC News, "This has nothing to do with religion." He says his son became angry after seeing 2 men kissing a few months ago in Miami, and he speculates that could have triggered his decision to kill.

Law enforcement says Mateen was well prepared, with an assault weapon, a handgun and 2 suspicious devices.

The NYPD tells TMZ, Mateen has no association with the department, and that the shirts he was photographed in were unofficial garments that could be purchased at any store.

50 people were murdered and another 53 injured inside Pulse nightclub in Orlando. It's the biggest slaughter at the hands of a gunman in American history.

Take a look at the pic below ... it's a police helmet with a bullet hole. The helmet saved the officer's life, although he suffered facial injuries.