Plus, we have to be practical here. If we're serious about prosecuting for perjury, we have to imprison every single cop who ever testified that shot an unarmed defendant/victim/whoever after they appeared to "reach for their waistband." Look for the phrase, cops use that specific language while testifying all the time. It's something cops say after they shot someone out of a completely irrational impulse, to make it seem like they had an objectively reasonable fear that the defendant/victim/whoever was about to pull out a gun. Even Darren Wilson said Michael Brown reached for his waistband...after being shot, running from the car, and presumably before reaching his hands out, or something. That doesn't even make sense! Actually, find me a cop who shot someone and DOESN'T use that exact phrase and I'll be shocked. It sounds so much better than "I freaked out and unloaded a clip."
Relatedly, wow does Darren Wilson's version of events sound like lies from front to back. I can accept that he may have acted in legitimate self-defense - much more likely, in my opinion, is that he shot Brown in objectively unreasonable self-defense, which would work out to something like voluntary manslaughter - but if it actually happened the way Wilson testified it did? I will eat my hat.