cold blood, in

Calculatedly ruthless. This expression comes from the days when it was commonly believed that blood rules the temper and was boiling hot when one was excited and ice-cold when one was calm. The French call it sang-froid, a term taken over in English with the same meaning. Thus Byron wrote of Don Juan, “Cross-legg’d with great sang-froid among the scorching ruins he sat smoking.” In more recent times Truman Capote used the term as the title of a detailed account (1965) of a deliberate act of murder