The Dain Curse by Dashiell Hammett

Owen Fitzstephan never spoke to me again. He refused to see me, and when, as a prisoner, he couldn't help himself there, he shut his mouth and kept it shut. This sudden hatred of me -- for it amounted to that -- had grown, I supposed, out of his knowing I thought him insane. He wanted the rest of the world, or at least the dozen who would represent the world on his jury, to think he had been crazy -- and did make them think so -- but he didn't want me to agree with them. As a sane man who, by pretending to be a lunatic, had done as he pleased and escaped punishment, he had a joke -- if you wanted to call it that -- on the world. But if he was a lunatic who, ignorant of his craziness, thought he was pretending to be a lunatic, then the joke -- if you wanted to call it that -- was on him. And my having such a joke on him was more than his egotism could stomach, even though it's not likely he ever admitted to himself that he was, or might be, actually crazy. Whatever he thought, he never spoke to me after the hospital interview in which I had said he was legally entitled to escape hanging.

His trial, when he was well enough to appear in court some months later, was every bit of the circus he had promised, and the newspapers had their happy convulsions. He was tried in the county court house for Mrs. Cotton's murder. Two new witnesses had been found, who had seen him walking away from the rear of the Cotton house that morning, and a third who identified his car as the one that had been parked four blocks away all -- or all the latter part of -- the previous night. The city and county district attorneys agreed that this evidence made the Cotton case the strongest against him.