A friend of mine, lawyer variety, told me of his client who, reeking drunk, ran off the road, wrecked, stumbled from the car, and passed out on the ground. In the particular jurisdiction, the cop has to see the drunk actually driving to convict him. The attorney used this to get the guy off, which means, since the driver was a lush, back on the road with you and me. This is what is wrong with adversarial system. Everybody involved knew the man was guilty, and knew he was dangerous to the public.
Truth takes a back seat to winning.
If he's assigned a case, he's expected to prosecute it. He in all likelihood won't know the guy to be innocent, though he may have doubts. As the case proceeds, he may have graver doubts. I think I'll drop the whole thing. Not good for the career, or for the ego, which has a lot to do with it.