An article in the April issue of Southwest Airline’s Spirit magazine explained the origin of various phrases.
The explanation of the “Third Degree” was traced to Freemasonry. Here is what the article said:
“In the 1880s, many of the higher-ups in New York City’s police force were Freemasons. The highest degree of initiation is the third degree, a process rumored to involve intense questioning.
One particularly successful NYPD interrogator was a third-degree Mason named Thomas Byrnes. In one New York Tribune article from 1883, he coined the phrase when he was quoted as breaking a gang of criminals by giving them ‘the third degree.'”
[Source: Masonic Information Center, June 2012]
Norm Leeper, PM, HA
Southern California Research Lodge