I'm also curious why he came to Boulder and to that particular King Soopers. Not surprisingly, he apparently has a history of mental illness, paranoia and violence... Maybe he thought someone was chasing him, so jumped on highway 93 or 36 to get away. Both exit very close to that KS. Total speculation on my part, but perhaps when he got there his appearance and demeanor drew attention that got integrated into whatever delusion he was having. After killing the first unfortunate person that looked at him wrong, could be he lost whatever little control he had left.
Trying to make sense out of the senseless is what most of us do, and hopefully shows us that we're not as irredeemably lost like this guy. People process trauma in different ways -- often mine is dark humor. I mean no disrespect to the lives lost or to those who are hurt by that loss, but ever since I saw pictures of the gunman being dragged away and wondered why he came here, a tasteless joke came to mind. Sorry in advance. See below, or stop reading now.
Maybe he bought a bad batch of Minoxidil at King Soopers that went to his head instead of his scalp.
Sorry again.