The story said that the door was open and they say the apartment in disarray. In Oklahoma there is what is called the "Plain sight clause" which applies to LEO's. It means that if a LEO can see something that is suspicious that is in plain sight, they have a right to enter and investigate. Which from the limited info that we have access to right now, that seems to be what happened. It is the same thing if you are growing pot in your house and you have your curtains open and a LEO walks by and sees it, they wont have to get a warrant to come in and take action, because it was in plain sight.
Just ask any LEO on here if what I say is correct. GC come on here and tell if my post is accurate.
Sorry dude but what happened here is not the same thing as plain sight of an illegal activity. Plenty of case law on those distinctions. Not saying they had no right to enter but works differently.