I straightened up. “Stop cribbing De Quincey and get on with it.”
He ignored me. “The artistic murder would be one in which the murderer is a sane person with a definite motive. Ideally it should never be suspected of being murder at all. Or, failing that, it should utterly confound the most up-to-date efforts of the autopsist and all the prying devices of the laboratory specialist in their attempts to prove that it is anything other than death from natural causes or accident. It should, preferably, be accomplished by a remote-control method having all the stark simplicity of an axiom out of Euclid. And the device used should not only be self-working but self-effacing, equipped, as was the device that caused Smith’s death, with an automatic vanishing attachment that leaves not the slightest vestige of anything remotely resembling a clue.”
“Hey,” Flint cut in, “you said this cigarette—”
“I know. It is a clue. But artistically it shouldn’t count. It’s a purely accidental blemish on a perfectly planned crime. The one other thing a criminal needs, the thing this criminal didn’t have quite enough of, is luck. If Dunning hadn’t happened to be smoking when he was hit, there would have been absolutely nothing to blow the gaff. Aristotle, Einstein, J. Edgar Hoover, and Clarence Darrow working together couldn’t have proved that the traffic smash was not a legitimate accident.”
Flint glared at him and started to interrupt. Merlini hastened quickly to the point. “Cigarettes don’t go out as a pipe does the moment you stop puffing at them. If you’ve ever left one on your wife’s polished dining-room table you will undoubtedly have had the point called to your attention. They go on burning merrily until there’s nothing left but ash and a charred streak on the veneer. Like that one.”
He pointed to the shortest of the burning cigarettes on the dish. Less than a half-inch of it remained. All the rest was ash.
“That’s been burning for eighteen minutes by my watch. But a good two thirds of the one we found in the car is unburned. Its neat, unwrinkled condition clearly indicates that it was not stepped on or snuffed out in the usual manner. What extinguished it?”
“It was lying on the floor of the car,” Flint said. “When the car crashed—”
“No.” Merlini shook his head. “It took that car fifteen minutes to get from here to where it cracked up. If the cigarette had been burning all that time, there’d be little more than a half inch left.”
“Then it went out when Dunning dropped—”
Merlini shook his head again. “I don’t think so. That’s why I’ve been tossing lighted cigarettes around this kitchen like a pyromaniac. They don’t go out quite that easily.” He pointed at the one stub in the dish that was not burning. “That’s the only one I put out in seven tries. It landed, and with more force than Dunning’s would have, directly on its lighted end. The burning portion was completely dislodged. Compare it with the one we found in the car. The burned center core of carbon is still intact. Why didn’t it continue to burn? What put it out somewhere between here and Mount Vernon?”
Flint gave him a quick look. “Does this have anything to do with the car heater you were so interested in?
Merlini nodded.
“But dammit,” Flint objected. “The heater was turned on. It was feeding a stream of air back into the car. That would help keep the cigarette lit. This stub looks more as if it stopped burning because of a lack of oxygen.”
“It did. Add that to Phillips’s statement that Dudley Wolff liked ice cream so much that there’s always a gallon freezer of it on hand.”
I saw it then. “Packed,” I finished, “with dry ice!”
“Yes. Frozen carbon dioxide. Someone with a neatly ingenious turn of mind shoved several sticks of it into the car heater. Too much of the oxygen in the hot-air stream coming back into the closed car was combined with carbon in the molecular proportion of two to one. Carbon dioxide is noncombustible. When the percentage of C02 in the atmosphere is too great a flame can’t get enough oxygen. Cigarettes go out. So do people. Same reason.”
Lieutenant Flint, in the butler’s pantry, was already examining the freezer.
“And,” Merlini continued, “note the irony. Mr. Zareh Bey Smith, the shallow-breathing expert, the man who couldn’t be asphyxiated, met his death after all primarily because of a lack of good fresh air. Dry ice is so called because, in melting at normal temperatures, it skips the liquid stage and passes directly from a solid to gaseous state. There’s no residue. That’s the automatic vanishing attachment I mentioned. And the car heater not only hastened the melting but fed the gas in a steady stream back into the car.”
I asked, “Why did you say the medical examiner wouldn’t find any traces of poison?”
“Because I sneaked a look in his toxicology text while Flint was talking to him. I quote: It is not possible to demonstrate carbon-dioxide poisoning by means of any chemical tests on the dead body. And, in the second place—”
“It won’t do,” Flint said as he returned. “You’d need a concentration of about twelve percent carbon dioxide in the air in that car. That would take a lot more dry ice than that heater would ever hold. A bucketful might do it, but not—”
“This murderer didn’t need that much,” Merlini said. “The second reason that the medical examiner will find nothing is that Smith didn’t die from C02 poisoning. He died from injuries received in the smash. The murderer not only used a poison undetectable to any medical examination even in lethal quantities — he didn’t even use enough to kill! He only needed enough to make Smith lose control of the car. The first symptoms of too much carbon dioxide are giddiness and a marked somnolence. You can’t mix those with a speed of seventy plus. When you travel that fast you need to be wide-awake just to stay on the road. Even if Smith noticed that the air seemed stuffy and that he was feeling sleepy, he had other more urgent matters to occupy his attention, namely: the cop that was on his tail.
“Smith blinked, tried to keep his eyes open, failed for an instant or two, and crashed. The CO2 dissipated when the car windows smashed. By the time anyone thinks to look in the heater, which we’d never have done anyway but for the accident of the cigarette, the dry ice has vanished into something as thin as, but more deadly than, air. I hope I never meet another murder device half as ingenious. Even if it fails, even if the victim isn’t in such an all-fired hurry, if he does have time to notice that something is wrong and opens a window, he’d never tumble to just what was wrong. He’d never know there: had been an attempt on his life. The murderer could try again and even use the same method.”
“All right,” Flint admitted doubtfully, “you make it sound good. But suppose I do take it? What have we got? One cigarette that might have gone out too soon and a hell of a lot of high, wide, and fancy guesswork. A defense attorney would have himself a picnic.”
He turned suddenly to me. “Harte, it’s your turn. What do you think you’ve got that tells you who the murderer is?”
“Motive,” I said, “and opportunity. Also a whole flock of answers to hard questions. The person who didn’t dig Smith up, the person who tried to get him with the trap gun, the person who did get him with the dry ice, the person who shot Wolff, and the one and only person who could have spirited that vest-pocket revolver out of the study is the one person we’ve consistently overlooked because—”