Prescription: Murder

Lt. Columbo: But one thing bothers me, Doctor. This man that we're talking about has taken a human life. Now wouldn't you say that he was insane?

Dr. Ray Flemming: Why? Because he committed an immoral act? Morals are conditioned, Lieutenant. They're relative, like everything else is today. Our murderer may be as sane as you and me. Killing may be repugnant to him, but if it's his only solution, he uses it. That pragmatism, my friend, not insanity.

Lt. Columbo: Tell me, Doctor, how do you catch a man like that?

Dr. Ray Flemming: You don't.

Lt. Columbo: You're probably right. He sounds just too clever for us. What I mean is, you know, cops, we're not the brightest guys in the world. Of course, we got one thing going for us: we're professionals. I mean, you take our friend here, the murderer. He's very smart, but he's an amateur. I mean, he's got just one time to learn. Just one. And with us, well, with us, it's - it's a business. You see, we do this a hundred times a year. I'll tell ya, Doc. That's a lot of practice.