From the article:
Police said the incident was recorded by surveillance cameras.
I would assume this means that there was a camera on the elevator and it caught it. I would hope that security was headed there before the lady pushed the emergency button in the elevator. For one of the thugs to have accidently stabbed his co-conspirator means he was stabbing as fast and as many times as he could.
This seems like a case that the defendants should probably plead guilty because it sure looks like the prosecution has all of the evidence they need. Whether they plead guilty or innocent, I hope the book is thrown at them if they are convicted. Incidents like this can affect future business not only for the Mandalay Bay but all hotels on the strip. There needs to be a clear message that this won't be tolerated.
I wish we knew more about the victims. Were they elderly? Were they frail?