Las Vegas police said Friday that the gunman who opened fire on a country music festival far below his hotel suite did not shoot a security guard six minutes before that rampage, contradicting a timeline they had offered earlier this week.

The change marked the latest shift in the official narrative of what happened before and during the massacre on Oct. 1. Authorities said the gunman, Stephen Paddock, fired from his high-rise suite in the Mandalay Bay Resort and Casino, killing 58 people and injuring hundreds more before killing himself.

Joseph Lombardo, the Las Vegas sheriff, also said Friday that the number of injuries related to the massacre had increased, rising to 546. Of that number, he said, 45 were still hospitalized, some in critical condition.

Investigators remain unable to determine a motivation for the rampage and why Paddock, a 64-year-old avid gambler, secretly ferrying 23 guns and other equipment into his room before opening fire. The FBI said Friday they had “made significant progress,” tracking thousands of leads and conducting hundreds of interviews.

But for much of this week, new questions surrounding the shooting have centered on the law enforcement response and the timeline, which had been changed multiple times and challenged by MGM Resorts International, the Mandalay Bay’s owner. The timeline and the law enforcement response have been thrown into question as police and the hotel offered different accounts of precisely what happened the night of the massacre.

Lombardo said he was “offended” at the criticisms he was taking and lamented the amount of time his investigators with the Las Vegas Metropolitan Police Department (LVMPD) had to dedicate to sifting through the timeline.

“There is no conspiracy between the FBI, between LVMPD and the MGM,” Lombardo said at a news briefing, during which he partially read from prepared statements and took no questions. “Nobody is attempting to hide anything in reference to this investigation. The dynamics and the size of this investigation requires us to go through voluminous amounts of information in order to draw an accurate picture.”

This latest timeline offered Friday still left key questions unanswered, including when police were first notified that there was a gunman firing from the hotel’s 32nd floor.

In the wake of mass casualty attacks, information relayed publicly often evolves and changes as authorities sift through large numbers of conflicting reports. But the accounts released publicly in Las Vegas have been remarkably fluid more than a week after the attack, with police and hotel officials offering significant — and at times conflicting — revisions to previous explanations of what happened.

The confusion began Monday when police said that the gunman fired at the hotel security guard, Jesus Campos, six minutes before the mass shooting began, not during the massacre as they had said. Lombardo also said police had hunted for the source of the gunfire and that officers responding to the gunman’s floor were unaware that a guard was shot until they arrived there, at which point the shooting rampage had ended.

MGM Resorts pushed back on this account, first saying Tuesday that there were unspecified inaccuracies and then, on Thursday, releasing a statement directly contradicting parts of what the police had said.

Lombardo had said Monday that Campos, the guard, was shot at 9:59 p.m. and that the mass shooting began at 10:05 p.m. This six-minute gap relayed by Lombardo left uncertain whether there was any lag in alerting police to the source of the gunfire during critical moments. Police said officers arrived on the 32nd floor at 10:17 p.m., two minutes after Paddock had stopped firing.

MGM, though, said it was “confident” that the 9:59 p.m. time was inaccurate and “was derived from a Mandalay Bay report manually created after the fact without the benefit of information we now have.” The company also disputed the suggestion of a lag, saying the shooting rampage began within a minute of Campos reporting his injury on the 32nd floor.

On Friday, Lombardo effectively agreed with the company’s statement, though he argued that the 9:59 p.m. time he had offered four days earlier “wasn’t inaccurate when I provided it.” Lombardo said he was told this time had been written by someone in a security log.

Upon investigation, Lombardo said, police learned that Campos first encountered a barricaded door on the 32nd floor at 9:59 p.m. The guard was eventually fired upon by Paddock “in close proximity to” 10:05 p.m., when the mass shooting began, Lombardo continued.

“He attempted to relay that information via his radio and it was confirmed because he also relayed that information via his cellphone,” Lombardo said. “So the timeline associated to both of those sources have been verified.”

However, Lombardo did not specify when police were informed about Campos’s report.

MGM has said that officers knew when Campos radioed it in. In a statement Thursday, MGM said “shots were being fired at the festival lot at the same time as, or within 40 seconds after, the time Jesus Campos first reported that shots were fired over the radio.”

The company said police officers “were together with armed Mandalay Bay security officers in the building when Campos first reported that shots were fired over the radio. These Metro officers and armed Mandalay Bay security officers immediately responded to the 32nd floor.”

However, MGM’s statement raised further questions, including why, if police and security “immediately” headed to the 32nd floor, police say their officers did not arrive there until 10:17 p.m. It also left unclear when the company believed Campos was shot or when the massacre began. A spokeswoman for the company did not respond to a request for comment on these questions.

Lombardo, who has previously said he believed the guard’s arrival may have caused the gunman to stop shooting, on Friday said Paddock had targeted officers during the massacre.

“The suspect was firing upon the crowd,” he said Friday. “As our officers started to arrive … it is readily apparent to me that he adjusted his fire and directed it towards the police vehicles.”

A look at the victims who died when a gunman attacked an outdoor country music festival on the night of Oct. 1. (Patrick Martin, Claritza Jimenez/The Washington Post)

Lombardo said he was not sure whether this meant Paddock had a vendetta against police or “was preventing the wolf from getting to his door sooner than later, but he chose to fire upon the police vehicles.”

On Friday, Lombardo said that investigators now think Paddock had fired at aviation fuel tanks near the concert purposefully, though these containers did not ignite. He also confirmed that contrary to previous police accounts, Paddock arrived at the hotel Sept. 25, not Sept. 28 as authorities had said.

Authorities have struggled to determine what, if anything, could emerge as a potential motivation for the shooting. Lombardo said an autopsy had been conducted on Paddock and “no abnormalities [were] observed visually,” though he said there would be further evaluation. The FBI said investigators had found “no signs of ideology or affiliations to any groups.”

The sheriff has defended the changes to the official timeline, saying this was because of police being transparent with the public. He has also warned it could change again.

Experts cautioned that it can take time for even basic information about what occurred during events like the one in Las Vegas to come together.

“I see this as being ridiculously hard on the people who are trying to get information out, get the totality of that story,” said Daniel J. Oates, who was the police chief in Aurora, Colo., when a gunman opened fire in a movie theater there in 2012. “This stuff takes time.”

Oates said Lombardo is dealing with a massive event that “eclipses anything prior,” noting the sheer number of people killed and injured, the way the gunman attacked and the venue where it occurred. He also said the sheriff is trying to balance an investigation with demands from the media and the public for information.

“I’m not surprised this is so difficult to manage . . . and that there are inaccuracies in reporting and things that have to be changed and corrected,” Oates, now the police chief in Miami Beach, said in a telephone interview Friday. “No one should take anything sinister from that on the law enforcement end. Everyone is trying hard.”

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This report, first published at 2:54 p.m., has been updated.