Even as investigators struggle to unravel the mystery of what motivated a gunman to open fire on a Las Vegas concert crowd, confusion surrounds the sequence of events in the fatal few minutes of the worst mass shooting in modern U.S. history.

On Thursday, the hotel where gunman Stephen Paddock opened fire from his high-rise hotel suite disputed the official timeline for the Las Vegas massacre and rejected any suggestion hotel officials delayed summoning police for several minutes after the gunman’s initial burst of fire.

It was the latest head-turning change in the investigation that has been frustrating for all involved. Since the Oct. 1 massacre, the timeline of the shooting has changed several times and police and hotel officials can’t seem to agree on the basics of when the shooting happened.

In the most recent chronology given by investigators on Monday, police said Paddock sprayed 200 rounds into the hallway on the 32nd floor Oct. 1, wounding an unarmed security guard in the leg, six minutes before he unleashed his barrage of bullets on the festival crowd. That raised a series of questions about whether officers were given information quickly enough to possibly have a chance to take out the gunman before he could carry out the bloodshed.

But on Thursday, MGM Resorts International, which owns the Mandalay Bay, said it was no more than 40 seconds between the time the guard used his walkie talkie to call for help and Paddock opened fire on the crowd from two windows in his suite.

The 64-year-old high-stakes gambler and real estate investor began his 10-minute attack on the crowd at 10:05 p.m., firing more than 1,000 rounds from his bashed-out windows, police said. Police didn’t arrive on the 32nd floor until 10:17 p.m., two minutes after he had stopped shooting.