Times Online
http://www.timesonline.co.uk/article/0,,564-1361452,00.html

November 17, 2004

Questions answered

When someone is given the “third degree”, what is it? What are the first and second?

In traditional Freemasonry, obtaining the first three “degrees” requires passing progressively more detailed cross-examinations about the tenets and rules of Freemasonry. For the third and most important degree (master mason) it is particularly detailed and lengthy.

As Masonry has been traditionally popular in law-enforcement agencies, “give him the third degree” became an “in” reference to a particularly gruelling police questioning.