The gunman behind the worst mass shooting in modern US history referenced the terrorist organization ISIS in a Facebook post moments before the massacre, a source close to the investigation told CBS News.
"You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance [sic]," Omar Mateen wrote, according to the source. "In the next few days you will see attacks from the Islamic State [ISIS] in the usa."
Mateen's account was deleted for violating Facebook's community standards, a source familiar with the matter told CNET.
Mateen was killed by police Sunday after shooting to death 50 people and injuring another 53 at the LGBT nightclub Pulse in Orlando, Florida. Mateen also declared allegiance to ISIS and leader Abu Bakr al-Baghdadi in 911 calls he made during the attack early Sunday morning, a US intelligence source told CBS News.
ISIS claimed responsibility for the shooting on the group's official radio station, al-Bayan.
The FBI is characterizing the shooting at Pulse as both a terrorist attack and a hate crime, CBS News' Paula Reid reported earlier Wednesday.