ARM by Larry Niven

and I thought I had it all.
    Peterfi folded his arms and said, “Well? What is it you want to search this time? Would you like to examine my legs?”
    “No, let's start with the insulin feeder on your upper arm.”
    “Certainly,” he said, and startled the hell out of me.
    I waited while he took off his shirt—unnecessary, but he needn't know that—then ran my imaginary fingers through the insulin feed. The reserve was nearly full. “I should have known,” I said. “Dammit. You got six months worth of insulin from the organlegger.”
    His eyebrows went up. “Organlegger?” He pulled loose. “Is this an accusation, Mr. Hamilton? I'm taping this for my attorney.”
    And I was setting myself up for a lawsuit. The hell with it. “Yah, it's an accusation. You killed Sinclair. Nobody else could have tried that alibi stunt.”
    He looked puzzled—honestly, I thought. “Why not?”
    “If anyone else had tried to set up an alibi with Sinclair's generator, Peterfi, you would have told the police all about what it was and how it worked. But you were the only one who knew that until last night, when he started showing it around.”
    There was only one thing he could say to that kind of logic, and he said it. “Still recording, Mr. Hamilton.”
    “Record and be damned. There are other things we can check. Your grocery delivery service. Your water bill.”
    He didn't flinch. He was smiling. Was it a bluff? I sniffed the air. Six months worth of body odor emitted in one night? By a man who hadn't taken more than four or five baths in six months? But his air-conditioning was too good.
    The curtains were open now to the night and the ocean. They'd been closed this afternoon, and he'd been squinting. But it wasn't evidence. The lights: he only had one light burning now, and so what?
    The big, powerful campout flashlight sitting on a small table against a wall. I hadn't even noticed it this afternoon. Now I was sure I knew what he'd used it for, but how to prove it?
    Groceries ... “If you didn't buy six months worth of groceries last night, you must have stolen them. Sinclair's generator is perfect for thefts. We'll check the local supermarkets.”
    “And link the thefts to me? How?”
    He was too bright to have kept the generator. But come to think of it, where could he abandon it? He was guilty . He couldn't have covered all his tracks—
    “Peterfi? I've got it.”
    He believed me. I saw it in the way he braced himself. Maybe he'd worked it out before I did. I said, “Your contraceptive shots must have worn off six months early. Your organlegger couldn't get you that; he's got no reason to keep contraceptives around. You're dead, Peterfi.”
    “I might as well be. Damn you, Hamilton! You've cost me the exemption!”
    “They won't try you right away. We can't afford to lose what's in your head. You know too much about Sinclair's generator.”
    “Our generator! We built it together!”
    “Yah.”
    “You won't try me at all,” he said more calmly. “Are you going to tell a court how the killer left Ray's apartment?”
    I dug out my sketch and handed it to him. While he was studying it, I said, “How did you like going off the roof? You couldn't have known it would work.”
    He looked up. His words came slowly, reluctantly. I guess he had to tell someone, and it didn't matter now. “By then I didn't care. My arm hung like a dead rabbit, and it stank. It took me three minutes to reach the ground. I thought I'd die on the way.”
    “Where'd you dig up an organlegger that fast?”
    His eyes called me a fool. “Can't you guess? Three years ago. I was hoping diabetes could be cured by a transplant. When the government hospitals couldn't help me, I went to an organlegger. I was lucky he was still in business last night.”
    He drooped. It seemed that all the anger went out of him. “Then it was six months in the field, waiting for the scars to heal. In the dark. I tried taking that big campout flashlight in with