It's always slipped to you in your drink, right? Rule 1 for college, never ever ever let your drink out of your hand. That's been known for 20 + years.
Not always, but it does happen. You said this "He advanced on the officer multiple times. Drugs or alcohol probably were a factor, but I am positive that no one forced it on the guy."
So you know he advanced the guy (police say so, must be true) and are positive that no one forced it on the guy. Were you with him? The only thing we know for sure is a naked college student was killed.
That being said you are most likely correct that it was drugs and he he took them knowingly. Usally the drugs in a drink thing have the opposite effect on people (date rape drugs). The reason I brought up drugs being given unknowingly is because it happened to someone I know when I was in college. I saw what it can do to someone. It was scary.