SOLVED. Crime Fiction about a guy forcing happy couples into a scenario where one has to kill the other to walk free or they both die. [s]

[Julia]

I think I read that book roughly 6 years ago. I also vaguely remember that one of the scenes might have involved couple in a sort of empty pool / whole that subsequently got filled with water to put them on a timer around either one killing the other because if they didn't they would drown together.
And they were not the only couple, I think murders of multiple ones are described. Unfortunately I do not even remember if it was a German book or an English one.

[Christine]

Is it fiction or true crime?

[Julia]

Christine wrote: "Is it fiction or true crime?"

It's fiction. Thank God :-D

[Kris]

Thanks. Added "fiction" to the topic header.

[Gerd]

The 50/50 Killer, this one sounds like it could be the one.

[Julia]

Yes! Solved! thanks a ton!