A citizen, who doesn't work for the police. Someone you may have known well, but they're just after you. They tell the police everything about you and your friends. They give the police any evidence they might have found or that you may have sold to them- drugs, weapons, etc.. These are the ones that can't be trusted.
I sold some drugs to my old friend John back in February. Then the police arrested me at my house 2 months later for a distribution charge. TRUST NO ONE.