To go scot-free (or to get off scot-free) is to get out of a situation, especially a legal one, without punishment or harm. The term tends to have negative connotations. We seldom use it when someone who is obviously innocent is cleared of charges. Instead, we use it when someone who is obviously guilty unjustly escapes punishment or does not face charges. For example, when a confessed bank-robber is cleared of charges on a technicality, we might say he got off scot-free. We probably wouldn’t say this of an accused bank-robber who is cleared of charges thanks to a squeaky-clean alibi and eyewitness testimony in his favor.
Scot-free is an old word. It derives from the Old English scotfre, which in Middle English became shot-free. The scot and shot in these old forms denoted a royal tax, so someone who was scotfre or shot-free was exempt from the tax. The modern sense, as well as the modern spelling, developed from these origins around the 16th century.
Because the scot in scot-free has nothing to do with Scotland or Scottish people or things, it does not need to be capitalized.
Besides this, the King granted and confirmed that their Lands in Thetford should be Scot free, and that they should have and enjoy the Liberties … [An essay towards a topographical history of the county of Norfolk, Francis Blomefield (1739)]
“Ugh! if they should let such a chap as that go scot-free, I, for one, should rather fancy speaking to Judge Lynch about it.” [“Little Molly White,” Fanny Forester, (1846)]
[I]t is a moral wrong that the burden of the risk necessarily incidental to the buisiness should be placed with crushing weight upon her weak shoulders and the man who has profited by her work escape scot-free. [The Rough Riders: An Autobiography, Theodore Roosevelt, 1899]
Other war criminals, he said, went “scot-free” because they were on ihe winning side. [New York Times (1961)]
Letting them off scot-free would be a blow to recent international efforts to bring to justice those who have committed systematic murder and torture. [The Economist (1999)]
Something I have never understood about child abuse in the Catholic Church is how those who cover it up get off scot-free. [Sydney Morning Herald (2012)]