Orlando Shootings: What We Know So Far

(CBS) -- The murder of 49 people inside a gay nightclub in Orlando is was the worst mass shooting in U.S. history.

So what do we know about the shooting?

• The attack was carried out by Omar Mateen. FBI Director James Comey said Monday that Mateen had been investigated by the FBI for 10 months, starting in May 2013. That investigation included surveillance and two face-to-face interviews.

• Mateen had "strong indications or radicalization," Comey said Monday.

• During 911 calls made by Mateen during the onslaught, the gunman pledged support for Islamic State as well as the Boston Marathon bombers.

• Comey told reporters on Monday that he was avoiding using Mateen's name, out of respect for the victims and to avoid glorifying the attack among other radicals.

• Orlando officials said that all of the bodies have been removed from Pulse nightclub.

• Hospital officials said five of the 53 people wounded in the attack were in "grave condition." A total of 29 people remain in the hospital.

• Mateen legally purchased the two guns he used in the last few days.

• Mateen was a licensed private security officer, who held a firearms license since at least 2011.