From this article
Zap2it: Your “Ripper Street” character, Fred Best, went from sleazy to heroic over three seasons. How was that to play?
David Dawson: I like to think of him as “ambitious” instead of “sleazy.” He was manipulating crime scenes, but he was hungry for the story. That was a real treat, to have an arc with such a surprise, so that the audience’s opinion is completely changed. When the writers told me about Season 3, how they wanted him to become a hero and go out with a real bang, I really appreciated that.