I got caught cheating once. Actually, not strictly cheating - I'd split from my girlfriend at the time, but it was pretty soon after the break and there was still some doubt as to whether we were going to get back together or not, and then I met this girl, and ... long story short, my ex was in the flat we'd shared together, picking up some of her things, when she spotted a pair of alien knickers on the radiator.

"Whose are these?" she asked.

"They're yours," I said, shrugging nonchalantly, like it was obvious.

"I'd recognise my own knickers, for Christ's sake. Just tell me whose they are."

"Ohhhh," I said, like it was all coming back to me, "remember I told you about that work trip I went on? Where we all went to Paris? Well, on the way back, a couple of people gave me their laundry, and I washed it, and it must've all got jumbled up with mine."

The trip to Paris was real. The laundry story clearly wasn't. I'd hoped the fact of the former would somehow obscure the lie of the latter. It didn't work.

"Why did they give you their laundry?"

"Huh? Oh. They don't have washing machines of their own, that's all," I shrugged again, chucking in a quick, "God, you're so suspicious!" for good measure.

At which point she started crying. In desperation, I'd adopted a "Dead Parrot Defence" - named after Michael Palin's lying shopkeeper in the famous Monty Python sketch. The Dead Parrot Defender is hoping that if they lie long and hard enough, reality itself will bend to accommodate them. Well, duh. It doesn't pan out that way, genius.

A classic Dead Parrot Defence consists of an overtly preposterous central premise cooked up in the heat of the moment (bonus points if it ignores a few well-known laws of nature), coupled with an obstinate, huffy denial of the facts. A few years ago, while trying to hide a smoking habit from a (different) girlfriend, I accidentally dropped a lighter on the bedroom floor. It rolled past her. She stared at it. And I indignantly claimed it had fallen through the ceiling, from the flat upstairs.

Until recently, Dead Parrot Defences have been the farcical preserve of adulterers hiding in cupboards and schoolkids whose dog ate their homework. But now things are getting serious. Recently, a spate of ridiculous alibis put forward by desperate murderers in high-profile cases has raised the art of the Dead Parrot Defence to awful, heartbreaking heights.

First, 37-year-old Mark Dixie confessed to having sex with teenage model Sally Anne Bowman's corpse, but denied being her killer. "All I saw was a pair of legs," he explained, "and I took advantage of her ... I thought she'd passed out drunk or fallen." In fact, she'd been stabbed seven times - although he claimed not to have noticed that. He only realised she was dead, he said, when she failed to react to him biting her repeatedly on the face and neck.

And last week, 27-year-old Karl Taylor denied murdering 31-year-old businesswoman Kate Beagley during a first date. His version of events ran as follows. Earlier that day, while in a "suicidal and despondent" mood, he'd borrowed a carving knife from a friend, hidden it up his sleeve and forgotten about it. That evening, he and Beagley were sitting on a bench drinking wine. The knife fell from his sleeve; he picked it up and put it on the seat. Moments later, while he was distracted by a phone call, she picked up the knife and stabbed herself 31 times in the face, neck and throat.

When the prosecutor handed Taylor a "knife" made of rolled-up paper and asked him to demonstrate precisely how Beagley took her own life, Taylor initially refused, saying he wasn't "in an emotionally fit state to do that", until the judge ordered him to do as he was told. When asked how long the incident had lasted, he replied "minutes".

"That's a very long time," noted the prosecutor, before asking why Taylor - a fitness instructor - hadn't attempted to stop her. The exchange that followed read like excerpts from a tasteless comic sketch.

"What am I going to do, use my martial arts to get the knife out of her hand?" complained Taylor.

"Why not?" asked the prosecutor.

"But it was an unanticipated situation," Taylor protested. "How was I going to take the knife out of her hand? What am I going to do, kick her unconscious? Your ideas are so outlandish."

"What's outlandish about suggesting you try to save her life?"

"I've already told you what I did. I stepped forward and stuck my hand out. It was an awkward situation to be in."

"It was an awkward situation to be in" would be a great final line if this was a sketch, not a real-life murder. By inadvertently turning their trials into jet-black farces, Dixie and Taylor added insult to injury. That's the trouble with the Dead Parrot Defence: it makes things worse.

It hurts more.

In which case, perhaps the punishment should fit the crime. Squeeze them into a grotesquely undersized cell and when they complain, shrug and say, "Sorry, the building's shrinking." Feed them nothing but gravel on toast, while claiming it's the latest gourmet trend. Offer them no-strings lifelong parole, only to withdraw it at the last minute because a dog ate the concept of liberty. Let them end their days as a comic victim, trapped within a prison of absurdist lazy lies. Yep. That'll do it.

· This week Charlie received a letter from Victim Support, sympathising with him for being the victim of an assault. Except he hasn't been the victim of an assault. Not yet anyway. What do they know that he doesn't?