WATCH: Investigators release terrifying body-cam footage from Las Vegas massacre
Law enforcement playing selected body-cam footage on a big-screen TV at a press conference.

During a press conference broadcast live by multiple outlets, law enforcement investigators played a disquieting video on a big screen, compiled of body-camera footage from police first responders.

Clark County Undersheriff Kevin McMahill introduced the edited montage and provided live narration of officers pinned down at the Route 91 Harvest country music festival, while other footage shows officers taking cover behind patrol cars on the famed Las Vegas strip.

During the press conference, authorities said they have now recovered 47 firearms that had been purchased by Stephen Paddock in Nevada, Utah, California and Texas.

Sunday night's mass shooting from the 32nd floor of the Mandalay Bay Resort and Casino was the deadliest in modern American history, with 59 fatalities and an additional 527 injuries.

Twelve of the firearms in Paddock's Mandalay hotel room allegedly had so-called 'bump stocks' that drastically increase the rate of fire by semi-automatic rifles.

Watch (warning: graphic)