Unknown Hour (2009)

Hynek Michánek wants to study medicine but fails his entrance exams five times. He starts a job as an orderly in a district hospital where one of the doctors on the examining board works as well. He feels no-one takes him seriously and he loathes the doctors, who treat him with disdain. When an old man begs him to end his pain and suffering by helping him to die, Hynek gives him a "liberating" injection. But now he has done it once, he finds he can't stop. He continues killing other patients, even though he knows he can't get away with it for long.

Unfortunately the movie Unknown Hour is not yet available on HBO Max.