1
general::
Phrase(s): in cold blood
Fig. without feeling; with cruel intent. (Frequently said of a crime, especially murder.) • The killer walked up and shot the woman in cold blood. • How insulting! For a person to say something like that in cold blood is just horrible.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
In a purposely ruthless and unfeeling manner, as in The whole family was murdered in cold blood. This expression alludes to the notion that blood is the seat of emotion and is hot in passion and cold in calm. The term therefore means not "in the heat of passion," but "in a calculated, deliberate manner." [Late 1500s]
American Heritage Idioms