The Alibi Machine
By Larry Niven


	McAllister left the party around eight o'clock.
	"Out of tobacco," he told his host apologetically. The police, if they got that far, would discover that that had been a little white lie. There were other parties in Greenwich Village on a Saturday night, and he would be attending one in about, he estimated, twenty minutes.
	He took the elevator down. There was a displacement booth in the lobby. He dropped a coin in the slot, smiling fleetingly at himself-he had almost forgotten to take coins- and dialed. A moment later he was outside his own penthouse door in Queens.
	He had saved himself the time to let himself in, by leaving his briefcase under a potted plant earlier this evening. He tipped the pot, picked up the briefcase and stepped back into the booth. His conservative paper business suit made him look as if he had just come from work, and the briefcase completed the picture nicely.
	He dialed three times. The first number took him to Kennedy International. The second to Los Angeles International. Long distance flicks required the additional equipment available only at what had once been airports: equipment to compensate for the difference in rotational velocity between different points on the Earth. The third number took him to Lucas Anderson's home in the high Sierras.
	It was five o'clock here, and the summer sun was still high. McAllister found himself gasping as he left the booth. Why would Anderson want to live at eight thousand feet?
	For the view, he supposed; and because Anderson, a freelance writer, did not have to leave his home as often as normal people did. But there was also his love of privacy- and distrust of people.
	He rang the bell.
	Anderson's look was more surprised than welcoming. "It was tomorrow. After lunch, remember?"
	"I know, but-" McAllister hefted the briefcase. "Your royalty accounts arrived this afternoon. A day earlier than we expected. I got to thinking, why not have it out now? Why let you go on thinking you've been cheated a day longer than-"
	"Uh huh." Anderson had an imposing scowl. He gave no indication that he was ready to change his mind-and McAllister had nothing to change it with anyway. Publishing companies had always fudged a little on their royalty statements. Sometimes they took a bit too much, and then a writer might rear back on his hind legs and demand an audit.
	The difference here was that Brace Books didn't know what McAllister had been doing with Lucas Anderson's accounts.
	"Let's just go over these papers," he said with a trace of impatience.
	Anderson nodded without enthusiasm, and stepped back, inviting him in.
	Did he have company? A glance into the dining nook told McAllister that he did not. A dinner setting for one, laid out with mathematical precision by one or another of Anderson's machines. Anderson's house was a display case of labor saving devices.
	How to get him into the living room? But Anderson was leading him there. It was not a big house, and a hostile publishers assistant would not be invited into the semisacred writing room.
	Anderson stopped in the middle of the room. "Spread it on the coffee table."
	McAllister circled Anderson as he reached into the briefcase. His fingers brushed papers, and then the Gyrojet, and suddenly his pulse was thundering in his ears. He was afraid.
	He'd spent considerable time plotting this. He'd even typed outlines, as for a mystery novel, and burned them afterward. He could produce the royalty statements; they were there in his briefcase, though they would not stand up. Or ... His hand, unseen within the briefcase, clenched into a fist.
	He was between Anderson and the picture window when he produced the Gyrojet.
	The Gyrojet: an ancient toy or weapon, depending. It was a rocket pistol, made during the 1960s, then discontinued. This one had been stolen from someone's house and later sold to McAllister, secretly, a full twelve years ago.
	A rocket pistol. How could any former Buck Rogers fan have turned down a rocket pistol? He had never shown it to anyone. He had had the thought, even then, that it would be untraceable should he ever want to kill somebody...
	The true weapon was the rocket slug. The gun looked like a toy, flimsy aluminum, perforated down the barrel. Anderson might have thought it was a toy-but Anderson was bright. He got the point immediately. He turned to run.
	McAllister shot him twice in the back.
	He left by the front door. He grinned as he passed the displacement booth. Fifteen years ago there had been people who put their displacement booths inside, in the living room, say. But it made burglaries much too easy.
	The alibi machine, the newspapers had called it then. They still did. The advent of the displacement booths had produced one hell of a crime wave. When a man in, say, Hawaii could commit murder in Chicago and be back in the time it would take him to visit the men's room, it did make things a bit difficult for the police. McAllister himself would be at a party in New York ten minutes from now. But first...
	He walked around to the back of the house and stood a moment, looking into the picture window.
	He'd thrown a paper tablecloth over Anderson's body. Glass particles on the body would be a giveaway. He'd take the tablecloth with him; and how were the police to know that it was the third bullet, rather than the first, that had shattered the picture window? But if it was the first bullet, then the killer must have been someone Anderson would not let into the house.
	McAllister fired into the picture window.
	Glass showered inward. There was the scream of an alarm.
	McAllister stood rooted. It was a terrible sound, and in these quiet hills it would carry forever! He hadn't expected alarms. There must be a secondary system, continually in operation-Hell with it. McAllister ran into the house, picked up the tablecloth and ran out. Glass particles all over his shoes. Never mind. His shoes and everything else he was wearing were paper, and there was a change of clothing in the briefcase. He'd dump gun and all at the next number he dialed.
	The altitude was getting to him. He was panting like a bloodhound when he closed the booth door and dialed. Los Angeles International, then a lakeside resort in New Mexico; the police could hardly search every lake in the country.
	Nothing happened.
	He dialed again. And again, while the alarm screamed to the hills, Help! I am being robbed. When his hand was shaking too badly to dial, he backed out of the glass door and stood looking at the booth.
	This hadn't been in any of the outlines.
	The booth wouldn't let him out. In all this vastness he was locked in, locked in with the body.

	It was two hours before the helicopter from Fresno arrived. Even so, they made good speed. Only a police organization could get a copter in the air that fast. Who else dealt with situations in which one could not simply flick in?
	The copter landed in front of the Anderson house, after some trouble picking it out of the wild landscape. Police Lieutenant Richard Donaho climbed out carefully as soon as the dust had stopped swirling. For the benefit of the pilot his face was unnaturally blank. The fear of death had taken him the instant the blades started whirling around, and it was only now leaving him.
	With the motor off, the alarm from the house was an intolerable scream. Lieutenant Donaho moved around to the side of the machine, opened a hatch and switched in the portable JumpShift unit.
	He stood back as men and equipment began pouring through. Uniformed men moved toward the house, spreading out. Donaho didn't interfere. He wasn't expecting anything startling. It was going to be cold burglary, the burglar vanished quite away.
	It was a smallish one-story house in a wild and beautiful setting, halfway up a mountain. The sun was still bright, though it had almost touched the western peaks. The sky was dark blue, almost lavender. Houses were scarce upslope, and far scarcer downslope. There were no roads. No roads at all. This place must have been uninhabited until twenty years ago, when jumpShift Inc. had revolutionized transportation.
	The shrill of the alarm stopped.
	In the sudden silence a policeman walked briskly from around the side of the house. "Lieutenant!" he called. "It's not burglary. It's murder. There's a dead man on the living room rug."
	"All right," said Donaho. He called Homicide.

	Captain Hennessey flicked in with the hot summer air of Fresno around him. It puffed out when he opened the door, and he felt the dry chill of the mountains. His ears popped. He stepped out of the belly of the copter, looking for the nearest man. "Donaho! What's happening?"
	Dopaho nodded at the uniformed man, whose name was Fisher. Fisher said, "It's around in back. Picture window shattered. Man inside, dead, with two holes in his back. That's as far as we've got. Want to come look, sir?"
	"In a minute. What was wrong with the displacement booth? Never mind, I see it."
	It was obvious even from here. The displacement booth was a standard model, a glass cylinder rounded at the top, with a dial system set in the side. Its curved door was blocked open by a chunk of granite.
	"So that's why you needed the copter," said Hennessey, "Hmm." He hadn't expected that.
	It was an old trick. Any burglar knew enough to block the displacement booth door before trying to rob a house. If he set off an alarm the police couldn't flick in, and he could generally run next door and use the displacement booth there. But here...
	"I wonder how he got out?" said Hennessey. "He couldn't set the rock and then use the booth. Maybe he couldn't use the booth anyway. Some alarms lock the transmitter on the booth, so people can still flick in but nobody can flick out."
	Donaho shifted impatiently. This was a murder investigation, and he had not yet so much as seen the body. Hennessey looked down a rocky, wooded slope, darkening with dusk. "Hikers would call this leg-breaker country," he said. "But that's how he did it. There's no other way he could get out. When the booth wouldn't send him anywhere, he blocked the door open and set out for. . . hmm."
	The nearest house was half a mile away. It was bigger than Anderson's house, with a pool and a stretch of lawn and a swing and a slide, all clearly visible in miniature from this vantage point.
	'To there, I think. He'd rather go down than up. He'd have to circle that stretch of chaparral..."
	"Captain, do you really think so? I wouldn't try walking through that."
	"You'd stay here and wait for the fuzz? It's not that bad. You'd make two miles an hour without a backpack. Hell, he might even have planned it this way. I hope he left footprints.
We'll want to know if he wore hiking boots." Hennessey scowled. "Not that it'll do us any good. He could have reached the nearest house a good hour ago."
	"That doesn't mean he could use the booth. Someone might have seen him."
	"Hmm. Right. Or...he might have broken an ankle anyway, mightn't he? Donaho, get that copter up and start searching the area. We'll have someone in Fresno question the neighbors. With the alarm blaring like that, they might have been more than usually alert."

Lieutenant Donaho had not greatly enjoyed his first helicopter flight, which had ended twenty minutes ago. Now he; was in the air again, and, the slender wings were beating round and round over his head, and the ground was an uncomfortable distance below.
	"You don't like this much," the pilot said perceptively. He was a stocky man of about forty.
	"Not much," Donaho agreed. It would have been nice if he could close his eyes, but he had to keep watching the scenery. There were trees a man could hide in, and a brook a man might have drunk from. He watched for movement; he watched for footprints. The scenery was both too close and too far down, and it wobbled dizzyingly.
	"You're too young," said the pilot. "You young ones don't know anything about speed."
	Donaho was amused. "I can go anywhere in the world at the speed of light."
	"Hell, that isn't speed. Ever been on a motorcycle?"
	"No!"
	"I was using a chopper when they started putting up the JumpShift booths all over the place. Man, it was wonderful. It was like all the cars just evaporated! It took years, but it, didn't seem that way. They left all those wonderful freeways for just us. You know what the most dangerous thing was about riding a chopper? It was cars."
	"Yah."
	"Same with flying. I don't own a plane. God knows I haven't got the money, but I've got a friend who does. It's a lot more fun now that we've got the airfields to ourselves. No more big planes. No more problem refueling either. We used to worry about running out of gas."
	"Uh huh." A thought struck Donaho. "What do you know about off-the-road vehicles?"
	"Not that much. They're still made. I can't think of one small enough to fit into a displacement booth, if that's what you're thinking."
	"I was. Hennessey thinks the killer might have set off the alarm deliberately. If he did, he might have brought an off-the-road vehicle along. Are you sure he couldn't get one into a booth?"
	"No, I'm not." The pilot looked down, considering. "It's too damn steep far a ground-effect vehicle. He'd leave tire tracks."
	"What would they look like?"
	"Oh, God. You mean it, don't you? Look for two parallel lines, say three to six feet apart. Most tires are corrugated and you'd see that too."
	There was nothing like that in sight.
	"Then, I know guys who might try to take a chopper across this. Might break their stupid necks, too. That'd leave a trail like a caterpillar track, but corrugated."
	"I can't believe anyone would walk across this. It looked like half a mile of bad stairs back there. And how would he get through those bushes?"
	"Crawl. Not that I'd try it myself. But they don't want me for the gas chamber." The pilot laughed. "Can you see the poor bastard, standing in the booth, dialing and dialing-"

	Lucas Anderson had been a big man. He had left a big corpse sprawled across a sapphire-blue rug, his arms stretched way out, big hands clutching. Anderson's arms had been dragging a dead weight. One of the holes in his back was high up, just over the spine.
	And men moved about him, doing things that would not help him and probably would not catch his killer.
	Someone had come here expressly to kill Lucas Anderson. He would have some connection with him, in business or friendship or enmity. He might have left traces of himself, and if he had, these men would find him.
	But the alibi machine might have put him anywhere by now. With a valid passport he could be in Algiers or Moscow.
	Anderson's bookshelf of his own works showed some science fiction titles. His killer could have been a spaceman-and then he could be in Mars orbit by now, or moving toward Jupiter at lightspeed as a kind of superneutrino.
	Yet they were learning things about him.
	The cleaning machines had come on as soon as the alarm had been switched off. An alert policeman had got to them before they could do anything about the mess.
	There was no glass on the body.
	There was no glass under the body either.
	"Now, that's not particularly odd," the man in the white coat said to Hennessey. "I mean, the pattern of explosion might have done that. But it means we can't say one way or another."
	"He could have been dead when the shot was fired."
	"Sure, or the other way around. No glass on him could mean he came running in when he heard all the noise. Just a minute," the man in the white coat said quickly, and he stooped far down to examine Anderson's big shoes with a magnifying glass. "I was wrong. No glass here."
	"Hmm. Anderson must have let him in. Then he shot out the window to fox us, and set off the alarm. That wasn't too bright." In a population of three hundred million Americans you could usually find a dozen suspects for any given murder victim. An intelligent killer would simply risk it.
	Someday, Hennessey thought when the black mood was on him, someday murder would be an accepted thing. It was that hard to stop. But this one might not have escaped yet
	"I'd like to get the body to the lab," said the man in the white coat. "Can't do an autopsy here. I want to probe for the bullets. They'd tell us how far away he was shot from, if we can get a gun like it, to do test firing."
	"If? Unusual gun?"
	The man laughed. "Very. The slug in the wail was a solid-fuel rocket, four nozzles the size of pinholes, angled to spin the thing. Impact like a .45."
	"Hmm." Hennessey asked of nobody in particular, "Get any footprints?"
	Someone answered. "Yessir, in the grass outside. Paper shoes. Small feet. Definitely not Anderson's."
	"Paper shoes." Could he have planned to hike out? Brought a pair of hiking boots to change into? But it began to look like the killer hadn't planned anything so elaborate.
	The dining setup would indicate that Anderson hadn't been expecting visitors. If premeditated murder could be called casual, this had been a casual murder, except for the picture window. Police had searched the house and found no sign of theft. Later they could learn what enemies Anderson had made in life. For now... '
	For now, the body should be moved to Fresno. "Call the copter back," Hennessey told someone. They'd need the portable JumpShift unit in the side.
	When the wind from the copter had died Hennessey stepped forward with the rest, with the team that carried the stretcher. He asked of Donaho, "Any luck?"
	"None," said Lieutenant Donaho. He climbed out, stood a moment to feel solid ground beneath his feet. "No footprints, no tracks, nobody hiding where we could see him. There's a lot of woods where he could be hiding, though. Look, it's after sunset, Captain. Get us an infrared scanner and we'll go up again when it gets dark."
	"Good." More time for the killer to move-but there were only half a dozen houses be could try for, Hennessey thought. He could get permission from the owners to turn off their booths for awhile. Maybe.
	"But I don't believe it," Donaho was saying. "Nobody could travel a mile through that. And the word from Fresno is that the only unoccupied house is two miles off to the side!"
	"Never a boy scout, were you?"
	"No. Why?"
	"We used to hike these hills with thirty pounds of backpack. Still...hmm." He seemed to be studying Donaho's face. "Is Anderson's booth back in operation?"
	"Yes. You were right, Captain. It was hooked to the alarm."
	"Then we can send the copter home and use that. Listen, Donaho, I may have been going at this wrong. Let me ask you something . . ."

	Most of the police were gone by ten. The body was gone. There was fingerprint powder on every polished surface, and glass all over the living room.
	Hennessey and Donabo and the uniformed man named Fisher sat at the dining table, drinking coffee made in the Anderson kitchen.
	"Guess I'll be going home," Donaho said presently. He made no reference to what they had planned.
	They watched through the window, as Lieutenant Donaho, brilliantly lighted, vanished within the glass booth.
	After that they drank coffee, and talked, and watched. The stars were very bright.
	It was almost midnight before anything happened. Then, i rustling sound-and something burst into view from upslope; a shadowy figure in full flight. It was in the displacement booth before Hennessey and Fisher had even reached the front door.
	The booth light showed every detail of a lean dark man in a rumpled paper business suit, one hand holding a briefcase, the other dialing frantically. Dialing again, while one eye in a shyly averted face watched two armed men strolling up to the booth.
	"No use," Hennessey called pleasantly. "Lieutenant Donaho had it cut off as soon as he flicked out."
	The man released a ragged sigh.
	"We want the gun."
	The man considered. Then he handed out the briefcase. The gun was in there. The man came out after it. He had a beaten look.
	"Where were you hiding?" Hennessey asked.
	"Up there in the bushes, where I could see you. I knew you'd turn the booth back on sooner or later."
	"Why didn't you just walk down to the nearest house?"
	The lean man looked at him curiously. Then he looked down across a black slope, to where a spark of light showed one window still glowing in a distant house. "Oh my God. I never thought of that."