By Monday, at least 58 people were dead and 515 were injured after a gunman opened fire from his 32nd-floor room at the Mandalay Bay Resort and Casino as Jason Aldean performed below.

Officials said 64-year-old Stephen Paddock was the man behind the deadliest mass shooting in modern U.S. history.

Some, like Phoenix-resident Tanya Groff recalled hearing what they thought of were fireworks while others heard screams and took off running.

RELATED: First victims identified in Las Vegas shooting

Videos from the scene captured a horrifying scene.

WARNING: The videos may be hard to watch.

LISTEN: Las Vegas police audio: Active shooter...many people down