The corporate owner of the high-rise Las Vegas Strip casino from which a gunman unleashed one of the deadliest mass shootings in modern U.S. history is squeezing a disputed police timeline of the start of the massacre down to seconds.

MGM Resorts International said in a statement Thursday that shots were fired into a music festival crowd “at the same time as, or within 40 seconds after” a security guard first reported by hotel dispatch radio that shots were fired.

The casino company says Las Vegas police accounts saying the casino security guard was wounded at 9:59 p.m. Oct. 1, and that gunfire out the hotel windows began 6 minutes later, are inaccurate.

The statement also says Las Vegas police and armed Mandalay Bay casino security officers were “in the building” when the guard reported the shooting and “immediately responded to the 32nd floor.”

Police have said the shooter, Stephen Paddock, fired a barrage into the hallway toward the guard and a casino maintenance worker, and fired assault-style weapons out the casino windows for about 10 minutes before killing himself with a gunshot to the head.