"Surely he will be put UNDER the jail for this one."
In the basement? What the hell does UNDER the jail mean?
It means there will be concrete above you and you'll never get out.
I have heard this expression all of my life. It is used to describe what will happen to someone in the most serious offenses, like passing a stopped school bus. They not only put you in the jail, they put you under it. Sorry, just assumed it was universal.