What's the origin of the phrase 'Scot free'?

Dred Scott was a black slave born in Virginia, USA in 1799. In several celebrated court cases, right up to the USA Supreme Court in 1857, he attempted to gain his freedom. These cases all failed but Scott was later made a free man by his so-called owners, the Blow family. Knowing this, we might feel that we don't need to look further for the origin of 'scott free'. Many people, especially in the USA, are convinced that the phrase originated with the story of Dred Scott.

https://www.phrases.org.uk/meanings/scot-free.html