I am not sure that you can necessarily equate intelligence with common sense and in addition to his 'Egghead' role he is also an actor and a bit of a drama luvvie!

It is all a big misunderstanding. He just tossed someone off into a canal.

"Common sense" is a myth, but its important to remember that being good or great at quizzes isn't really intelligence, its a factor more defined by education.

Education and intelligence probably correlate, but they aren't the same thing. Criminals, no matter how well educated, tend towards being caught by their mistakes. A common factor of crime, in all humans, is that most people who plan a crime, plan the crime in intricate detail, but not how to get away with it.

Very successful criminals, tend to have either been lucky (on hitting on a very good after the crime plan) or have poor planning on committing the crime, but excellent planning on how to get away with it.

In truth, pretty much anyone can commit most crimes. The real art is in determining how to keep getting away with it - and this is, according to forensic scientiets, the really difficult part.

His publisher must have really hated him to have told him that admitting to a murder in print wouldn't be a problem.

You can be convicted of a murder without a body or a witness. However there has to be someone on the radar ad a victim . E.g. a missing persons inquiry which is unsolved and evidence to suggest they are dead at someone elses hand and not their own.

So one of several things has happened.
1. He did do it
2. He is aware of someone going missing at that time, the mystery of which has never been solved and he had decided to claim it as a murder he has committed.
3. The whole things is pure fantasy.

Either way it sounds as though he has some serious mental issues. Either because he has decided to admit to murder in a book when he had absolutely no reason to do So or because he is a complete fantasist

Classic sociopathic behaviour. Attention seeking - and it looks like it has got peoples' attention.