The Mercy Protocol - J. R. Vale

The Mercy Protocol is a dark conspiracy thriller set inside a New York ICU.

A senior doctor has been quietly ending the lives of terminal patients for twelve years - convinced it's mercy, not murder. Then patients who should have survived start dying on his ward, using methods that mirror his own. He can't go to the police without exposing himself. So he has to find the killer alone, from the inside, while a sharp homicide detective closes in and a brilliant young resident starts connecting dots he cannot afford to have connected.

It's a book about the distance between intention and consequence - and what happens when a man who has always been certain he's doing the right thing is forced to confront someone who believes exactly the same thing, for entirely different reasons.