Massacre in Orlando: A Timeline of Terror (Photos)

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.