Fenton nodded, his fingers still tapping on the file. "You'd naturally expect him to be right about one or two things, even if they didn't appear in the papers. He's no dumb-bell. He couldn't have written those juvenile delinquency articles and foster-fathered a major movie if he was. He'd naturally be pretty good at guessing games. It's always the exceptions which strengthen, lend real weight, to that kind of rule."
Fenton cleared his throat. "It's like in medicine. You take a very rare, unusual kind of disease. Say there are twenty symptoms which are very diagnostic of that particular disease. But one of them only occurs in one case of the disease out of a hundred. And the patient has that one symptom, along with the others. Now ... let's say that in the whole United States, in the course of the year, only about two hundred people die of that rare disease.
"Don't you see what I'm driving at Gallison—or do you? It would have to mean that only about two people die from that disease with that particular symptom attached to it every year out of a nation of a hundred and seventy-five million people. According to the law of averages, how likely would the patient be to have the disease? The very symptom which does sometimes occur in connection with the disease—but rarely—which you might think would strengthen the diagnosis, actually helps to weaken it, to make it so unlikely as to practically eliminate the possibility that the patient could have it."
"So it's medicine he's talking about now," Gallison said, unable to keep a slight trace of acidity out of his voice, but wishing, almost instantly, that he hadn't spoken at all.
"I only used that as an example," Fenton said, his voice sharpening slightly. "But it spells the difference between a crack medical diagnostician and a bad one. It's always those little, subtle intangibles you have to take into consideration. And that's really just another way of saying you have to have imagination to be either a good cop or a good doctor."
A slightly wistful look came into Fenton's eyes. "I sometimes wish I'd taken up medicine. Healing people is much better than wallowing in the kind of ugly—Oh, well, skip it."
"But you can't clear a self-confessed murderer completely on that basis alone," Gallison protested. "His confession could be off in a hundred ways, and he could still be guilty. At least ... it would remain a possibility. You practically just admitted that yourself. If we had other evidence ... and we do have a little additional evidence ... we could still take it before a jury."
"You mean the DA could," Fenton said, his voice becoming tinged with the kind of impatience a grammar-school teacher might have displayed toward a pupil who had just pulled a boner in geography. "What are you trying to do—add to our burdens? The DA could take it before a jury, all right. But he'd get his ears pinned so far back that the next time he ran for election it would be as a dog-catcher. Did you ever hear of an alibi, Gallison? Or is that too involved a point of law for you?"
Lieutenant Fenton sighed heavily and his voice softened a little. "Sorry, Gallison. That was a lousy thing for me to say. But at least you know that I wasn't pulling rank on you. It's something I've never done or never will do—unless you come in here and toss your badge on the desk and I have to hand it back to you and tell you to go through channels."
"Okay, Joe. I understand. Don't let it worry you."