What do you do if someone attacks your credibility?

Q: Officer, did you actually see my client fleeing the scene?

A: No sir. But I subsequently observed a person matching the description of the offender, running several blocks away.
Q: And who provided this description?
A: The officer who responded at the scene.

Q: A fellow officer provided the description of this so-called offender. Do you trust your fellow officers?
A: Yes, sir. With my life.
Q: With your life? Then let me ask you this Officer. Do you have a room where you change your clothes in preparation for your daily duties?
A: Yes sir, we do.

Q: And do you have a locker in that room?
A: Yes sir, I do.
Q: And do you have a lock on your locker door?
A: Yes sir, I do.

Q: Now why is it, Officer, if you trust your fellow officers with your life, you find it necessary to lock your locker in a room you share with these same officers?
A: You see, sir … we share the building with the court complex, and sometimes lawyers have been known to walk through that room …

I can see where the lawyer was going with that line of questioning, but he had no chance after that comeback.