'20/20' INVESTIGATES THE UNANSWERED QUESTIONS AND REMAINING MYSTERY SURROUNDING THE MASS SHOOTING IN LAS VEGAS

'20/20: Mystery in Las Vegas' Airs on the West Coast Saturday, November 4 (10:00 - 11:00 p.m. PDT), on ABC

Following the mass shooting at Las Vegas' Route 91 Harvest country music festival leaving 58 people dead and some 500 others injured, "20/20" investigates the unanswered questions that still remain. The hour features ballistics and forensics experts attempting to unravel the perplexing mystery behind the deadliest shooting in modern American history. "20/20" reports on the shifting timeline of the attack; the search for gunman Stephen Paddock's motive, the tick-tock of his movements in the week leading up to the shooting; his missing hard drive; the hotel security guard's encounter with Paddock; and conspiracy theories and whether any of them have any validity. "20/20" also looks at the longtime girlfriend of Paddock, Marilou Danley. The hour includes Interviews with Danley's brother, Paddock's friends and neighbors, and a litigator representing families of victims and survivors who have filed lawsuits. "20/20" follows up with a woman who lost her husband and survivors who are coping with their new normal. Correspondent Matt Gutman and Chief Investigative Correspondent Brian Ross report. Due to the college football broadcast schedule, "20/20: Mystery in Las Vegas" airs only on the West Coast Saturday, Nov. 4 (10:00 - 11:00p.m. PDT), on ABC. (Rebroadcast: ABC OAD: 10/27/17)

"20/20" is anchored by Elizabeth Vargas and David Muir. David Sloan is senior executive producer.