He admitted keeping victims in steel boxes. Were they dead or alive? Yes & no. He sent the police a letter to explain: ψ.

 

Solution.

The suspect was Professor Rudy Applebaum. Three of his graduate students had gone missing, Dennis Lee, Ranbir Kapur, and Amelia Quirke.  They had all been on their way to see him at the time of their disappearance. But no bodies had been found. Nothing, as yet, could be proven.

Professor Applebaum was the archetypal mad professor. Wiry hair all over the place, bottle-end lenses in his glasses, shapeless jumpers, insane giggle, staring eyes, an over-excited manner and a tendency to spit and dribble as he spoke. All the classic signs were there. He also had an annoying habit of speaking in riddles.

Detective Inspector Stafford wasn’t standing for it. “What have you done with them?”

“An interesting question, Inspector, though perhaps the real question is, What haven’t I done with them? Doesn’t it occur to you that I may have both done something with them and not done something with them?  It may be true to say that I have killed them. It may also be true to say that they are still alive.”

“Look, matey, I never went to university, so I don’t appreciate all that doublespeak.”

The professor gave a manic giggle. “Technically, it’s not doublespeak. Doublespeak is when you say one thing but mean something else. I said two things and meant them both.”

“I give up,” said Stafford. He turned to his second-in-command, DS Ringer. “You have a go, son.” To Applebaum, he added: “Detective Sergeant Ringer is a graduate.”

Ringer  grimaced at Applebaum’s mocking laughter. “Professor, how can you say two different things and mean them both?”

“Have you never heard of Schrodinger’s cat?”

“Who’s Schrodinger?” cut in Stafford.

“Will you tell him or shall I?” said Professor Applebaum. “Or perhaps we should both? Or neither of us? Or both of us and neither of us. Perhaps we should let Schrodinger’s cat tell him.”

“I’d like you to tell us,” said Ringer.

“Schrodinger was an Austrian physicist who came up with a thought experiment. You know what thought is?”

“There’s no need to take that tone,” said Stafford.

“His experiment consisted of imagining a cat enclosed in a steel box with a radioactive material, a Geiger counter and a canister of hydrocyanic acid. If one of the atoms of the radioactive material decays, the Geiger counter registers it and breaks a canister releasing the hydrocyanic acid which kills the cat. The probability of this happening within a given time, an hour say, is equal to the probability of it not happening. Expressed as a psi-function of the entire system, it’s true to say that as long as the steel box is closed, the cat is both dead and alive at the same time. It is only when you open the box, that the cat is discovered to be either dead or alive.”

“It was you who sent us the Greek letter? The ψ?” said Ringer.

“Of course. What did you read at university?”

“Philosophy.”

“Philosophy? Well, you should have been able to work it all out when you received the ψ.”

“What have you done with them?” Stafford thumped the table as he barked the question.

“I have recruited them to help me in an experiment of my own. I have recreated the conditions suggested by Schrodinger. Not in my head – in the basement of the physics department! Thought experiments are for pussies!”

“What do you mean, you’ve recreated the conditions?” asked Ringer.

“Oh, come on. You’re a graduate. You should be able to work it out for yourself.”

“You mean you have a sealed steel box, containing  a Geiger counter, with a small amount of a radioactive substance and a poisonous gas canister.”

“Actually, there are three steel boxes. One has to be able to replicate one’s results.”

“And there are cats in the boxes? The students are monitoring what happens?” Ringer was hopeful.

“Well, no. Schrodinger’s experiment was always objected to on the grounds of cruelty to animals. So I replaced the cats with graduate students.”

“Right. Let’s get over there and get them out,” said Stafford, rising from his seat.

“Wait, Inspector!” cried Applebaum. “Don’t you see? While they are in the boxes they are at least both dead and alive. If you open the boxes, they will be either dead or alive. Are you prepared to take that risk? Isn’t it better that they exist in this strange dual state, rather than committing them to the possibility of death? You might save them, or you might kill them by opening the boxes.”

Professor Applebaum began to make miaowing noises. He bunched his fists like paws and licked the side of his hand, rubbing it over his face, like a cat grooming herself.

“I don’t need this,” said Stafford, shaking his head. “It’s Christmas Day. I should be at home with Mrs Stafford, opening up presents, not this mad man’s steel boxes.”

“Welcome to the post-Newtonian universe,” said DS Ringer.

“And you can shut it,” said DI Stafford.