Orlando terror suspect Omar Mateen in an undated photo. He is the gunman behind the deadliest shooting in U.S. history, which claimed 50 lives.

Mateen entered Pulse, a popular LGBT night club with an intent to kill. Around 2 a.m., he began shooting patrons with an assault rifle.

About 20 minutes into the shooting, Mateen placed a 911 call pledging allegiance to ISIS and referencing the Boston Marathon bombers. First responders arrived on the scene to find carnage inside and outside the club.

Around 5 a.m., authorities broke down a wall and exchanged gunfire with Mateen, who had taken hostages. Mateen was killed.

During a morning press conference, Orlando mayor Buddy Dyer amended the casualties from 20 to 50. Thirty-nine (including Mateen) were found dead at the club, two died outside, and nine died en route to the hospital. Fifty-three were injured.

Pulse remained an active crime scene Sunday as authorities worked to identify the victims.

Authorities descended upon Mateen's apartment Sunday afternoon to collect evidence and find a motive behind the shooting.

A bomb squad was also brought in to sweep for explosives.

Family and friends of the victims continue to await word. Authorities have yet to notify many next of kin.