Updated at 10 a.m. ET Wednesday

More than a week after a gunman opened fire on a concert in Las Vegas, killing 58 people and leaving hundreds of others injured, authorities say those chaotic minutes around the Mandalay Bay hotel are still coming into focus — and some of their findings have apparently been disputed by hotel officials.

At a news conference Monday, Clark County Sheriff Joe Lombardo revised one of the key details on the reported timeline of events that night: when exactly shooter Stephen Paddock injured Jesus Campos, the unarmed Mandalay Bay security guard who came to investigate his floor.

"What we have learned is Mr. Campos was encountered by the suspect prior to [Paddock's] shooting to the outside world," Lombardo said. He told reporters Monday that Paddock shot Campos at 9:59 p.m. local time on Oct. 1, roughly six minutes before turning his gun on the crowd at the Route 91 Harvest music festival.

"Immediately upon being injured, [Campos] notified security of his situation," Lombardo said. He added that Campos also prevented a maintenance worker from being shot. But Lombardo also acknowledged that police "weren't aware of [Campos] being shot until they met him in the hallway after exiting the elevator" onto Paddock's floor.

As the Los Angeles Times reports, officials had previously suggested that Paddock stopped firing upon the arrival of Campos, who was investigating an alarm about another open door on the shooter's floor.

The revision to the timeline raises new questions about the timing of the police response — and about why Paddock stopped shooting around 10:15 p.m., if it was not Campos' intervention that caused him to do so. According to police accounts, there was more than an hour between the moment the gunfire ended and the moment officers breached and entered Paddock's room, at about 11:20 p.m.

By the time officers entered the room, police say Paddock had already killed himself. Lombardo acknowledged Monday that "we do not know why at this point" the gunfire from his room halted as early as it did.

MGM Resorts International, the company behind Mandalay Bay, cast some doubt Tuesday night on this new timeline — without clarifying what details, in particular, are in dispute.

"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 [sic], and we believe what is currently being expressed may not be accurate," company spokesman Debra DeShong said in a statement.

"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," she added. "Therefore, it is not appropriate for us to comment further at this time on what remains an open matter for law enforcement."

Lombardo, for his part, cast the revision Monday as one of a number of "minute changes" that are common in an evolving investigation.

"As I have conveyed to you from the very beginning," Lombardo told reporters, "in your zest for information and my zest to ensure the public safety and the calming of their minds — some things are going to change."

Still, Lombardo was clear that another prevailing question remains: Why did Paddock decide to carry out the attack in the first place?

"As I've said from Day 1, we want to figure out the 'why' to this, and we'd like to know the motive," Lombardo said. "That is our most important goal to prevent any further action associated with any other individual who is contemplating this or what exactly went on in the suspect's mind to enable him to pull off such a complicated event."

And that "why" continues to elude them.

"This individual purposely hid his actions leading up to this event," Lombardo said, "and it is difficult for us to find the answers to those actions."

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