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 are still coming into focus. At a news conference Monday, Clark County Sheriff Joe Lombardo revised one of those key details: 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 that "we do not know why at this point" that gunfire ended — but he cast the revision as one of a number of "minute changes" common to 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.

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