Not Columbo

It had probably been the abattoir, thought Leslie daFox, sitting in the back of the police van.  His wrists were handcuffed together and his hands cupped each other in his lap.  Opposite him, sitting on a narrow plastic bench with odds stains along it, was a burly policeman who was glaring at Leslie.  He had little piggy eyes set deep in a fat, florid face, a sparse, mousey-brown moustache that had been waxed into rat-tails at the ends, and acne that ran from under his chin down his neck and disappeared into a shiny, greasy-looking uniform jacket.
"Do you know why you're under arrest?" said the policeman.  This was the first time he'd spoken since he'd heaved his bulk into the van and Leslie had slid slightly along his bench as the van wobbled and tilted.  There's a faint aroma of cinnamon in the air; presumably the policeman had been eating and had had to break off from his lunch so that he could come and talk to Leslie.
"No," said Leslie.  He looked the policeman directly in his eyes, wondering what colour they were.  They were too shadowed to make out, and his eyebrows were sprouting making it harder still.
"Really, Mr. daFox?"  The policeman rolled his r but otherwise sounded rather bored.
"Really," said Leslie pleasantly.  Then, almost as an after-thought, and just when he thought the policeman would be about to speak, he added, "unless you think you're Peter Falk, of course."
"Who?"  The policeman conjured a small notepad and pencil from an inside pocket.  "How do you spell that?"
Leslie obligingly spelled the name and the policeman wrote it down, tore the page off, and clambered to the end of the van to open the doors and pass the paper to someone outside.  Leslie craned his neck but he couldn't see past the policeman.  Then the man returned, breathing a little heavily as though he'd been running to pass off the note.
"Right," he said, sitting back down again and rocking the van alarmingly.  "Why do you think you'd have been arrested if I were Peter Falkland?"
"Peter Falk," said Leslie.  "And if you were he, you wouldn't have arrested me.  But if you thought you were he, you might have arrested me, by way of demonstrating that you were definitely not he."
"...what?"
"Look," said Leslie, still keeping his patience.  "Three months ago two students were found dead in a lecture theatre I was scheduled to teach a class in.  Since then you've been hounding me like you think I know where the doughnut-leprechaun lives; you've had Tweedledum and Tweedledee bodyguarding me, for some risible value of bodyguard, and every so often someone phones me up at 2am and demands to know who I'm going to kill next.  The number they call from matches the one on the business card you gave me when you first found the bodies.  This is police harassment, and I think arresting me is just the latest escalation of it."
"Right," said the policeman.  "Tweedledee and Tweedledum?  Is that an Alice in Wonderland reference?"
"Through the Looking Glass, I think," said Leslie, suddenly appalled with himself that he couldn't remember.  "Not original either, I'm afraid, but it went down rather well with test audiences back in the seventies, so it's a deserved cliché."
"Is that clichet with a 't'?"
"No.  No 'y' either."
"And the doughnut-leprechaun?"
"May be real, but I don't know where he lives," said Leslie.
"Ha.  Ha."
Someone banged on the back-doors of the van and pulled the door open.  A young policeman with a shock of black hair spiked up impossibly high on his head peered in, and spotted the fat policeman.
"Peter Falk?" he shouted, making Leslie flinch.
"Yes?" said the policeman, glaring at Leslie as though daring him to try and make a break for it.
"Dead," said the young policeman.  He pulled his head back and closed the doors of the van.
"Dead," said the fat policeman.  "You're thinking I should be dead, are you, Sir?  And you found coming out of an abattoir and all...."
"Oh dear God," said Leslie hopelessly.