Description: "The third degree" is an idiom for intense, rigorous, or aggressive questioning. Ever wonder where this phrase actually comes from? There are a few theories. The most likely: it comes from the brutal interrogation tactics of New York police commissioner Thomas Byrnes, who led the police force in the 1880s, and was known for his brutal interrogation techniques. The phrase may have been a pun based on Byrnes’ name and “third degree burns.” (Byrnes was a firefighter before he became a policeman.)