It makes sense that the darker side of the Rebellion is getting the spotlight in this series, since it was also part of Cassian's backstory in Rogue One. The original trilogy makes the Rebels all seem like good-hearted, plucky freedom fighters, but there always had to be their share of spies, assassins, and saboteurs among them.

I remember Cassian saying that he and the other Rogue volunteers had all done terrible things for the Rebellion, and they all just wanted to make sure it was to accomplish something rather than give everything up to run and hide.

And this is where it all starts.