Overkill. Literally.

Killing your wife is a terrible, heinous, immoral act, even if she has been nagging you for years. 

But it takes an especially evil man to build an electric chair in order to kill his wife. 

What was this guy thinking?

Did he think the electric chair wouldn't be noticed by the police?

Was he going to tell authorities that she had accidentally jammed a fork in an outlet?

Had Mr. Castle conducted his own private trial, found her guilty and sentenced her to death?

Thankfully, his wife didn't fall for his electric chair bit and managed to escape. 

It probably looked too much like an electric chair.  

And then, as if to guarantee the bizarre nature of the story, Mr. Castle attempted suicide by cutting his wrists open with a knife when he had a perfectly good electric chair available. 

Poor planning and not so great under pressure.  Not exactly the qualities you look for in an effective killer.