Crime Orlando Shooter Called 911 During Massacre Pledging Allegiance to ISIS, Was 'On Radar' of FBI Before Shooting: Reports A federal law-enforcement official tells PEOPLE: 'The FBI was aware of this guy before today. He was on their radar' By Adam Carlson Published on June 12, 2016 01:40 PM Share Tweet Pin Email Photo: Gerardo Mora/Getty Soon after a gunman opened fire at a popular gay nightclub in Orlando, Florida, killing at least 49 people and injuring at least 53, he called 911 and pledged allegiance to ISIS, a federal law enforcement official tells PEOPLE. The gunman, reportedly identified as Omar Saddiqui Mateen, first called 911 about 2:30 a.m. local time, approximately 30 minutes after opening fire at Orlando’s Pulse, the official says. On that call, he announced he was shooting up the club and claimed he was armed with explosives – a claim which authorities have not confirmed and which they are “still exploring,” the official says. “The 911 operator, using reverse-call technology, called back the gunman and it was then that he pledged allegiance to [ISIS leader] Abu Bakr al-Baghdadi” the federal official tells PEOPLE. The gunman “also mentioned the Tsarnaev brothers,” who orchestrated the Boston Marathon bombings of 2013, the official says. The nightclub attack is the deadliest mass shooting in American history, according to authorities. • Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter. Federal investigators have confirmed the gunman, a U.S.-born citizen, had yet-unspecified “ties to Afghanistan,” the federal official tells PEOPLE. Authorities have said they do not yet know a motive. However, the official says that Homeland Security, the FBI and intelligence officials had, before this weekend, noted two separate occasions – Ramadan and Pride Month – for which they had separate intelligence that some kind of attack was to be “expected.” “We are pursuing those two threads,” the official says. Shooter Was ‘On Radar’ of FBI The federal law-enforcement official tells PEOPLE of the shooter: “The FBI was aware of this guy before today. He was on their radar.” Mateen’s father told NBC News this morning the shooting “has nothing to do with religion,” and instead pointed toward his son’s recent anger at two men kissing as a possible cause. An FBI spokesperson said Sunday morning that this is an ongoing investigation and wouldn’t classify it as a terror or hate crime at this time.