Witnesses are worthless. The majority of people out there have their heads stuffed so far up there that they don't realize anything is going down until it's too late. People are just completely clueless.
And then there's the fact that witnesses are completely unreliable. You have five people witness the same event, something that surprises them and gives them some stress like a shooting, and you'll get five different stories, and nary a one will be backed up by evidence. Heaven forbid there's video, then the odds of any of that five being 100% right is pretty much zero.
Situational awareness is very important.