Investigators plumbing Stephen Paddock's life in search of answers have been so far unable to explain what motivated him to carry out the rampage, why he stopped shooting and whether he planned even more carnage beyond the Mandalay Bay Resort and Casino.

In recent days, a new level of uncertainty has emerged in the case, as questions also emerged about the law enforcement response to the shooting after police revised their account of what happened before and during the massacre.

Ten days after the shooting, key details about what unfolded remain a mystery, while officials cannot seem to agree on basic facts about the timeline.

Police in Las Vegas, who had previously said Paddock shot a hotel security guard during the rampage, reversed course Monday and said the guard was actually wounded six minutes before the mass shooting began.

The revelation from Joseph Lombardo, the Las Vegas sheriff, gave way to a new round of questions, including when information about this shooting was relayed to hotel security and when — or if — that detail was then given to the local police. So far, neither the police or the hotel have offered any answers, and both sides have in fact suggested there could be future revisions to the timeline.

"Nobody's trying to be nefarious, nobody's trying to hide anything, and what we want to do is draw the most accurate picture we can," Lombardo said in a television interview Wednesday. "I'm telling you right now, today, that that timeline might change again."

MGM Resorts, which owns the Mandalay Bay, released a statement Tuesday night casting doubt on the latest timetable Lombardo had announced. In the statement, the company said it "cannot be certain about the most recent timeline" released publicly "and we believe what is currently being expressed may not be accurate."

MGM did not elaborate on what part of the police timeline was inaccurate and did not respond to questions regarding what it was disputing, what happened inside the hotel and whether hotel security officials are required to immediately call the police upon reports of gunshots. Through a public relations firm, MGM declined to make any employee available for an interview Wednesday, and said in a statement: "Security has been and continues to be a top priority at all of MGM Resorts."

The Las Vegas police did not respond to a list of questions Wednesday about the revised timeline or whether they stood still by it. During his interview with 8 News Now, a local TV affiliate in Las Vegas, Lombardo attributed shifting timeline to police being transparent.

"We're letting people know exactly what we know at the time we know it," he said. "The other thing is, there's more than 20,000 moving parts associated with this investigation. And it takes time, and I ask people to give us patience. "

Lombardo also said the timeline could shift again due to the "human factor," explaining that it was possible someone reporting the time the first shots were reported could have not written down the correct time. Earlier this week, Lombardo had said Jesus Campos, the guard, "immediately" notified hotel security about his wound at 9:59 p.m. - six minutes before the gunman began firing a 10-minute barrage of bullets into the crowd below.

"It may condense smaller, it may be less than 6 minutes when it's all done," Lombardo said. "But let's not get wrapped around the axle on that."

Precisely when the shots were fired and whether police were told before the shooting began - prompting officers to search the hotel - could be critical, as experts have long said that the key during active shootings is to find and stop the attacker.

"Time is always of the essence once the gunfire starts, because more time means the potential for more people to get injured," said Peter Blair, executive director of the Advanced Law Enforcement Rapid Response Training Center and a criminal justice professor at Texas State University.

Paddock had assembled an arsenal of 23 guns in his room and set up cameras to monitor the hallway, police said. Police previously said he shot Campos during the rampage and suggested that Campos' arrival may have interrupted the shooting.

Police arrived on the Mandalay Bay's 32nd floor at 10:17 p.m., two minutes after Paddock stopped firing for reasons that Lombardo said remain unknown. Lombardo has defended the police response, saying in his television interview Wednesday that officers "did everything right" in responding and chafing against questions that have been raised.

"I think people are looking for a fall guy, as usual as a result of post-evaluation of any critical incident, and there isn't one there," he said. "No matter what the timeline is, the response was as quick as possible, and I don't think the response could have been any faster."

NBC News published an audio recording Wednesday that appears to capture a building engineer who was also on Paddock's floor saying that someone was "firing a rifle on the 32nd floor down the hallway" and asking for them to call the police.

Stephen Schuck, the engineer, told the "Today" show Wednesday morning that he had been on a higher floor before being called down to "check out a fire exit door that would not open." He credited Campos, who shouted for him to take cover, with saving his life.

"The rounds started coming down the hallway," he said. "I could feel them pass right behind my head."

Schuck said he called in the shooting on the radio and was with Campos when police arrived on the floor, directing them to where Paddock's room was.

When gunfire is confirmed at a casino or a room, hotel security's next move is to summon police as quickly as possible, said David Shepherd, former head of security at the Venetian Resort Hotel and Casino in Las Vegas.

"Once you have confirmed gunfire, you call in police," said Shepherd, who is chief executive of the Readiness Resource Group, a crisis management and critical infrastructure firm. "Immediately. Get 'em in as fast as you can."

Shepherd, whose son is a Las Vegas city marshal who responded to the shooting, said that he can only remember a handful of shootings happening on casino property in his 36 years in the city.

Sgt. Kevin Fair, a spokesman with the Atlantic City police in New Jersey, said that his department responds to any incidents of gunfire, whether inside a casino or otherwise. Fair noted that reports of gunfire inside casinos were also rare, though he did not have an exact number.

"In the event of shots fired within a casino, we will be notified immediately and patrol officers will be dispatched to the location," Fair wrote in an email. "We have the capabilities within our police department to not only talk directly with casino security over a radio system, but to take control of their surveillance cameras."

The shooting has prompted a lawsuit against makers of the "bump stock" devices on Paddock's guns, and it is likely to spark further legal action. The first known suit against MGM in this case was filed Wednesday in Clark County District Court on behalf of Paige Gasper, who was attending the country music festival and struck with a bullet that shattered her ribs and lacerated her liver, according to the lawsuit.

The complaint accuses MGM, along with Paddock's estate and other entities, of negligence in "failing to maintain the Mandalay Bay premises in a reasonably safe condition" for not responding quickly enough to Campos's shooting or noticing Paddock's preparations.

In a statement, Debra DeShong, the MGM spokeswoman, said the company's focus remained on supporting people impacted by the shooting and cooperating with law enforcement.

"Out of respect for the victims we are not going to try this case in the public domain and we will give our response through the appropriate legal channels," DeShong said.

Local police and the FBI continue to probe the shooting, speaking to Paddock's relatives and retracing his steps. The Justice Department said in a statement Wednesday it would give Nevada $1 million "to assist with the immediate costs of responding to the mass shooting in Las Vegas.''

Lombardo said investigators were still developing a picture of Paddock, and he noted Wednesday in his interview that some things about the case may remain forever unknown.

"There's going to be questions that will never get answered," he said. "I'm sure of that."

The Washington Post's Devlin Barrett contributed to this report.