تعریف و معنای "blood on {one's} hands"

What is the origin of the idiom "blood on one's hands" and when to use it?

The idiom "blood on one's hands" has roots in biblical references, such as the story of Cain and Abel, and has been further popularized through its usage in literary works like Shakespeare's Macbeth. It is commonly employed in discussions about war crimes, acts of violence, or situations where individuals or groups are seen as directly responsible for the loss of lives or inflicting pain.