Mandalay Bay staff did not call Las Vegas police until after Stephen Paddock had already begun firing on the concertgoers, according to "World News Tonight" on ABC.
ABC's information comes from an anonymous source who has reviewed records from the hotel-casino.
According to the report, Mandalay Bay staff did not call police when security guard Jesus Campos reported internally that someone was shooting on the 32nd floor. Nor did they call police when building engineer Stephen Schuck also reported internally that someone was firing at him on the 32nd floor.
About six minutes after shots were fired inside the hotel, Paddock began firing outside at the crowd, according to Sheriff Joe Lombardo.
MGM Resorts spokesperson Debra DeShong wrote in a statement on Tuesday that the company does not believe this timeline is accurate:
This remains an ongoing investigation with a lot of moving parts. As evidenced by law enforcement briefings over the past week, many facts are still unverified and continue to change as events are under review. We cannot be certain about the most recent timeline that has been communicated publically, and we believe what is currently being expressed may not be accurate.
We understand the public’s desire for information and the importance of getting our community and the public at large the information they deserve, and we are doing everything we can to support law enforcement’s efforts to do so. Therefore, it is not appropriate for us to comment further at this time on what remains an open matter for law enforcement.
Las Vegas police say they'll have an updated and more complete timeline on Friday.