In the hours following the massacre, the worst in modern U.S. history, Mateen's father, Seddique Mir Mateen, described to NBC News his son's alleged homophobia and how it may have motivated the attack.
"We were in downtown Miami, Bayside, people were playing music. And he saw two men kissing each other in front of his wife and kid, and he got very angry," Seddique Mir Mateen told NBC News. "They were kissing each other and touching each other, and he said: 'Look at that. In front of my son, they are doing that.' And then we were in the men's bathroom, and men were kissing each other."
Authorities are also investigating an apparent connection between Mateen and the Islamic State, who has since claimed responsibility for the shooting.
Following Sunday's violence, victims' families, the LGBT community, their allies, and supporters from around the world gathered to mourn victims at impromptu vigils. These are just some of the most moving images to have been released so far.