I can’t claim credit for this - I heard it on the radio a while ago. I think that it was suggested by PD James. It’s almost perfect, except that you need an accomplice. It’s also rather UK-specific.
Suppose you want to kill your wife.
You suggest that she takes a trip to France. A booze cruise for instance.* She tells all her friends. You tell all yours. Everybody knows that she is going.
Meanwhile secretly recruit an accomplice that looks enough like your wife to fool a casual observer.
The night before your wife is due to leave, fouly MURDER her. Dispose of the body. Apparently there are always ways to do this - building sites, forests etc. I’m sure that an enterprising murderer could manager it.
Here’s the clever bit: you give your wife’s passport to the accomplice. She then goes to France in your wife’s place! She then comes back with her OWN passport.
Wait a day or two. Report that your wife hasn’t contacted you. Act upset. Cry.
The whole missing persons investigation will then be conducted in France. Records will show that she went but never returned. You were in England the whole time and as such have the perfect alibi.
The accomplice is, however, a problem. You could murder her too (murdering strangers is, I suspect, a lot easier to get away with. OTOH maybe she would be tied to you in some way, so that she would never tell (lover?) Or if she is remote enough a stranger from somewhere far enough away she may never piece together the crime. I leave this bit as an exercise for the reader.
There. What do you think?
*Note for Merkin readers: alcohol is much cheaper in France than England. This has lead to lots of people in the South-East of England buying ferry trips to France with the sole intent of hopping over the Channel, buying up lots of beer and wine and then driving back again. You can bring back truckloads, as long as you persuade the authorities that it is all for private consumption. This practice has become known as a “booze cruise”