Why did Omar Mateen murder 49 people at the Pulse nightclub in Orlando, Florida?

After Omar Mateen's murderous rampage on June 12, 2016, much of the discussion of Mateen's motives centered on speculation of whether he was a closeted gay man and whether his prime motive was hatred of gay people. Speakers at a vigil I went to in Ithaca in June argued that his murderous homophobia was caused by fundamentalist Christian homophobia, toxic masculinity, misogyny, and the American empire. One speaker even felt the need to mention Palestine as a target of the evil American empire. (How this had anything to do with Mateen's rampage was unclear to me, but the audience clapped nonetheless). None of the speakers asked whether his allegiance to ISIS might have been a reason for his rampage. In fact, ISIS wasn't even mentioned.

Evidence that came soon afterwards called into question this construction of events. On June 20, 2016, the FBI released the transcript of the first conversation that Mateen had with the 911 operator. At first, they redacted the murderer's mentions of ISIS, but after an uproar, they produced the complete transcript. Twice, he pledges his allegiance to the leader of the Islamic State. This is the transcript, from the Wall Street Journal:

2:35 a.m.: Shooter contacted a 911 operator from inside Pulse. The call lasted approximately 50 seconds, the details of which are set out below:

Orlando Police Dispatcher (OD)

Omar Mateen (OM)

OD:     Emergency 911, this is being recorded.

OM:     In the name of God the Merciful, the beneficial [in Arabic]
OD:     What?

OM:     Praise be to God, and prayers as well as peace be upon the prophet of God [in Arabic]. I let you know, I’m in Orlando and I did the shootings.

OD:     What’s your name?
OM:     My name is I pledge of allegiance to to Abu Bakr al-Baghdadi of the Islamic State.
OD:     OK, What’s your name?

OM:     I pledge allegiance to Abu Bakr al-Baghdadi of the Islamic State may God protect him [in Arabic], on behalf of the Islamic State.

OD:     Alright, where are you at?

OM:     In Orlando.

OD:     Where in Orlando?

[End of call.]

Today, the police released the audio of the conversations between Mateen and the 911 operator (http://www.nytimes.com/2016/11/01/us/911-recordings-gunman-orlando-nightclub-siege.html). The Times reported:

Before he was killed by the police, Mr. Mateen declared his allegiance to the Islamic State and complained about American airstrikes in the Middle East. “What am I to do here when my people are getting killed over there?” Mr. Mateen, 29, asked the negotiator in their first conversation. “You get what I’m saying?”

In an earlier article, he New York Times said:

The F.B.I.’s account of the emergency calls included no mention by Mr. Mateen of any hatred of gays or a desire to attack a gay nightclub in particular; the bureau has been investigating the attack as a possible anti-gay hate crime, but the material released on Monday offers nothing to back up that theory.

If the police and FBI investigations found no evidence that suggested that Mateen was a closeted gay man, or even that anti-gay animus motivated his choice of target, it seems to me that our narrative about his murders needs to change. He did not murder forty-nine people in Orlando because he hated gay people, or because of fundamentalist Christianity or the American army empire. He killed them because of his allegiance to the murderous Islamic State, which has also horribly murdered thousands of innocent people in Iraq and Syria.