Authorities said that the shooting suspect mailed letters to University of Nevada, Las Vegas employees across the country and that at least one letter contained an unidentified white powder.
Lawyers for survivors and victims wanted the company held liable for negligence for having allowed the gunman into an MGM-owned hotel with luggage full of weapons and ammunition in 2017.
"Throughout his life, [Stephen] Paddock went to great lengths to keep his thoughts private, and that extended to his final thinking about this mass murder," officials said on Tuesday.
In October 2017, a gunman fired from his room at the Mandalay Bay in Las Vegas, killing 58 people and injuring hundreds. Now MGM, which owns the hotel, is asking the courts to declare it not liable.
Police released video in response to a lawsuit from media organizations. It shows the tense moments as officers try to find out where the shots are coming from and as they search the hotel.
Defendants in the suits include MGM Resorts International, which owns the Mandalay Bay, and Live Nation, the organizer of the country music festival at which 58 people were killed last month.
After he was shot, Jesus Campos yelled "Take cover!" at a hotel engineer and a guest as the Las Vegas gunman sprayed bullets into the hall. His account added detail to the timeline of events Oct. 1.
At issue is whether the hotel was delayed in calling police after the shots were first reported by hotel security staff.