MGM Resorts, which owns Mandalay Bay, contested the police department’s announcement in a statement on Tuesday, saying that the company “cannot be certain about the most recent timeline” and that “what is currently being expressed may not be accurate.” It did not provide further details, citing the continuing investigation.

Here is what we know and what we don’t know about the police response to the shooting:

When did the security guard arrive and what was he responding to?

Mr. Campos arrived on the 32nd floor shortly before 10 p.m. to investigate an alarm indicating that a door to a room — not Mr. Paddock’s — was open. While he was there, Mr. Campos heard drilling noises coming from Mr. Paddock’s room. Sheriff Joseph Lombardo said Mr. Paddock was most likely using a drill to set up cameras or to place a rifle.

What did the guard do after he arrived?

At 9:59 p.m., six minutes before Mr. Paddock began shooting at the crowd, Mr. Campos was investigating the drilling noise when Mr. Paddock fired roughly 200 bullets through the door of his room. One responding police officer told “60 Minutes” that the door looked like “Swiss cheese” afterward.

It is unclear where in the hallway Mr. Campos was standing and how close to the door he was when he took the fire. Mr. Campos, who was wounded in the right thigh, retreated from the doorway and immediately told casino security personnel that he had been shot. When the police arrived, Mr. Campos directed officers to Mr. Paddock’s room and helped hotel guests evacuate until he was told he needed to seek medical attention himself.

Sheriff Lombardo said last week, before the timeline changed, that Mr. Campos’s “bravery was amazing.” When the chronology was adjusted on Monday, the sheriff stressed that Mr. Campos had immediately alerted his bosses about the gunman and then protected a maintenance worker who arrived on that floor. It is not known when and how the hotel security officials informed the police that Mr. Campos had been shot.