Someone who commits a mass murder.

(US, colloquial) murder in the first degree.

A murder in which organs or other body parts are harvested for the production of traditional medicine

A murderer will always be discovered. / (idiomatic) Secrets or hidden crimes will eventually be exposed or discovered; nothing that is secret can remain a secret forever.

plural of murder simulator

(derogatory) A graphic action video game that features killing as an important component.

Alternative form of murder hole / A deep pit used for drowning malefactors as a punishment.

plural of murder board

(informal) A committee of questioners set up to review a proposal and/or to help someone prepare for a difficult oral examination.

A slit or hole above the entrance to a fortification, thought to provide access for defenders to kill invaders.