Full coverage: 50 Dead in Orlando Nightclub Shooting
Islamic State has claimed to be behind the attack, though US authorities say they have no clear evidence of the link just yet. It is however, being investigated as an act of terrorism. Authorities have also revealed that the FBI had actually questioned the shooter a couple of years back, and more than once.
US Federal authorities believe the triggerman in Orlando's mass shooting on Sunday may have been inspired by ISIL. This, after a 9-1-1 call before the shooting spree in which 29-year old Omar Mateen reportedly pledged his allegiance to the Islamic group.
Speaking after the shooting, U-S President Barack Obama said he has instructed the FBI to investigate this as an act of terrorism.
"I've directed that we must spare no effort to determine what, if any, inspiration or association this killer may have had with terrorist groups," Obama said.
The classification of Sunday's shoot as terrorism now allows Federal authorities to access specific metadata to try to trace down: who the shooter was speaking to, when, what he was reading, and how often. The terror classification also makes this the deadliest attack on U-S soil since 9/11.
Authorities had actually interviewed Mateen in previous years, on at least two separate occasions.
In 2014, they say, they were investigating his communications with Moner Abu Salha, a U-S national who traveled to Syria to train with Al Qaeda's Al Nusra Front, then returned to the U-S, then ... went back to Syria, and carried out a suicide bombing, the first American to do so in Syria's ongoing civil war.
The investigation did not lead authorities to consider Mateen an active threat.
But on Sunday, the ISIL-linked Amaq News Agency released this statement, saying the club attack was carried out by an Islamic State fighter.
It was reminder to many of the December 2015 shooting spree in San Bernardino, California. A husband and wife - believed to be influenced by radical Islam - gunned down 14 people at a holiday work party, before being killed by police.
