Calculatedly ruthless; in a deliberate cruel manner. Without feeling or pity

 When a Congressman makes the extraordinary claim that U.S. troops killed innocent civilians "in cold blood," Washington takes notice. And when he's a former Marine and decorated Vietnam vet, the assertion carries special weight

Quando un deputato americano dichiara ufficialmente che le truppe americane hanno ucciso civili innocenti “a sangue freddo”, Washington deve prendere nota. E quando questo deputato è anche un ex marine e un reduce decorato del Vietnam, la dichiarazione pesa molto di più

Who can ever forget watching on live-TV Jack Ruby busting through a ring of bodyguards to shoot down Lee Harvey Oswald in cold blood? On live TV!

Chi potrà mai dimenticare la scena in diretta TV di Jack Ruby che si fa largo tra un nugolo di guardie del corpo per uccidere a sangue freddo Lee Harvey? In diretta!

I could never kill an animal in cold blood, let alone a human being!

Non potrei mai uccidere un animale a sangue freddo, men che meno un essere umano!

This expression, that dates back to the late 1500s, comes from the days when it was a common belief that blood was the seat of emotions and was hot when one was excited and cold when one was calm