His father, Seddique Mir Mateen, also told NBC News that his son was angry at the sight of two men kissing in Miami a few months ago, which may have motivated his attack on Pulse, a gay nightclub in Orlando.
President Obama spoke to both motivations in his first remarks on the shooting, telling Americans on Sunday afternoon "this was an act of terror, and an act of hate."
The president added, "we've reached no definitive judgment on the precise motivations of the killer."
While investigators may take weeks to establish the killer’s exact motivations, leaders of America’s gay community are already speaking out about the devastating impact of a mass murder at a gay nightclub in the middle of gay pride month. The attack comes as California authorities say they thwarted a plot to bomb the L.A. Pride festival on Sunday.
Stuart Milk, an LGBT leader and nephew of Harvey Milk, told MSNBC, "June 12 will live forever as one of the darkest days for the LGBT community."
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Hate crimes targeting gay Americans are a common problem, second only to race as a target of hate, though they rarely occur in bars or nightclubs.
According to the most recent FBI statistics, for the year 2014, there were 1,017 hate crimes against gay Americans — or 18.6 percent of all hate crimes. That includes 65 in Florida.
About 2 percent of the national hate crimes occurred in gay bars or nightclubs, according to the FBI.
After Sunday’s attack, the Human Rights Campaign stated that "22 percent of all hate crimes in Florida" are based on sexual orientation, "trailing only race as the most common motivation," according to data from Equality Florida.
Mass shootings often reignite the policy debate over access to guns, and hate crimes present another fault line in that debate.
In most states, people convicted of misdemeanor hate crimes may still legally purchase guns.
The majority of states “have not enacted laws to prevent convicted misdemeanant hate criminals from having easy access to guns," according to a 2016 report, "Hate and Guns," by the Center for American Progress.
As for Mateen, he was able to legally purchase firearms within the past week, according to the ATF. Federal authorities had twice investigated him for potential links to terrorism, the FBI said, but no ties were confirmed.
Under federal law, it takes far more than a terror review to bar someone from legally purchasing guns.
To be legally barred from buying firearms for criminal activity, under federal law, an individual must be convicted of a felony.
As Americans process the Orlando attack and politicians weigh in, the jarring mix of Islamic terrorism, anti-gay hate and domestic gun policy is sure to stoke many debates in the days to come.
For the deadliest attack on U.S. soil since September 11, 2001, one fitting tribute began Sunday evening at Ground Zero in New York, where the skyscraper was shining with rainbow colors.
"I am directing One World Trade Center to be lit the colors of the pride flag in a tribute to LGBT Americans and the lives that were lost," said New York Governor Andrew Cuomo in a statement, adding, "an attack on one is an attack on all."