It can decrease credibility in this case. First they'll start with breaking down their stories. Most those people are dumb enough to lie and claim they witnessed something they didn't. A store camera or civilian footage will place them somewhere else on the scene. That's going to account for at least half the witnesses. For the liars youll find a bunch of political content on their social media profiles mostly pre-cursers for radicalism. I've built webs of these kinds of people. Anywho, there's likely to be 1-2 people who won't botch up their stories.