The White House and FBI said Monday that the Orlando gunman, Omar Mateen, was a “homegrown extremist” who was “radicalized” through the internet. Mateen burst into the Pulse gay club on Sunday, where he opened fire and fatally shot at least 49 people and injured 53 before he was shot dead by a SWAT team.

President Barack Obama, after meeting with security officials, told reporters in Washington, D.C., that the 29-year-old, responsible for the deadliest mass shooting in modern U.S. history, was “inspired by various extremist information that was disseminated over the internet.”

The president added that there was no clear evidence to show that he was directed externally, reportedly saying: “As far as we can tell right now, this is certainly an example of the kind of homegrown extremism that all of us have been so concerned about for a very long time.”

During the shooting, Mateen had made a 911-call, in which he reportedly pledged his allegiance to the Islamic State group (also called ISIS). But FBI Director James Comey said Mateen had expressed support for multiple armed Islamist movements and people, which “adds a little bit to the confusion about his motives.” 

The American-born gunman’s ex-wife said Sunday that he may have been mentally ill while his father, Seddique Mir Mateen, said Monday his son may have acted out of anti-gay sentiments. The gunman's father told reporters that the massacre was “the act of a terrorist” and adding: “I apologize for what my son did. I am as sad and mad as you guys are.”

President Obama said that the massacre raised the issue of terrorism and gun control, and that both issues must be equally addressed.

“If we have self-radicalized individuals in this country, then they are going to be very difficult to find ahead of time, and, how easy it is for them to find weapons is, in some cases, going to make a difference as to whether they are going to be able to carry out attacks like this,” he said.

Comey said tracking lone wolf attackers like Mateen was like finding “needles in a nationwide haystack.” He added that authorities were also trying to work out what kind of people could become radicalized.

The Orlando Medical Centre reportedly said Monday that a number of victims who were being treated there remained critically ill, and five patients were in a grave condition.