yeah he mentions to jyn how she wasn't the only one to lose everything and how he'd been fighting in the war for a long time and I feel like he lost his moral compass in that for a while.I'd bet it wouldn't be the first time he's killed though. He said he's done stuff he's not proud of before. Wouldn't doubt he's carried out assassinations before.
I'm still holding out hope that Jar Jar came up on that beach and saved Jyn and Cassian and they're chilling in a cave with Luke on whatever planet he's hiding on at the end of episode 7