The MGM timeline means that the police were in the Mandalay Bay BEFORE the shooting began. This is why they have screwed around with the timeline and originally had the security guard shot after the outside shooting. But, MGM says that the police were with hotel security when the guard reported in about the shooting. That's why they didn't call the police. The police were already there. That means the police were in the hotel when the security guard called in. So, if he was shot after the shooting began, that allows the police to have come in after the shooting began. But, with him shot before the shooting began, the police are in the hotel before the shooting began, and that is difficult to explain, isn't it?