Warning! SPOILERS for Star Wars: Andor episodes 1-3Although Diego Luna's Cassian Andor displayed his capability as a killer in set five years before Rogue One: A Star Wars Story and the events of A New Hope. That being said, viewers shouldn't necessarily expect Cassian to become more heroic and noble just because he's been recruited into the early Rebellion.
In Star Wars: Andor episode 1, Cassian was searching for his sister whom he hasn't seen in years since he was taken from their homeworld of Kenari. However, he ended up on the wrong side of two CorpSec officers who tried robbing him at gunpoint. During the resulting brawl, one of the agents was inadvertently killed which motivated Andor to brutally shoot the other in the desperate hope of covering his tracks. That being said, it was clear Andor was conflicted and felt as though he had no choice.
However, Andor's well-received episode 3 sees Cassian being helped by Stellan Skarsgård's Luthen Rael who sees his potential to become a Rebel and "fight the Empire for real." Evading the CorpSec task force assembled to bring Andor to justice, Cassian had his opportunity to kill Syril Karn, catching him by surprise and putting a blaster to his head. While Luthen encouraged Andor to kill the officer and even offered to kill Karn himself, the episode ends with Syril being spared while the two Rebels make their escape. As such, this encounter implies that Cassian doesn't want to kill if he feels he has a choice. However, that will likely change as the prequel series continues.
Don't Expect Andor To Be More Heroic, Despite Not Killing Officer Karn
Andor sparing Karn's life despite killing a different agent in the premiere showcases Cassian's complicated morals. Likewise, he's yet to ground himself within Luthen's cause in Andor, the spark of resistance that will soon grow into the full-fledged Rebellion. Once that happens, Andor will likely start becoming more willing to take a life for the Rebel cause. This is evidenced by his character at the beginning of Rogue One where he kills his informant as well as his orders to assassinate Galen Erso which he would have carried out if not for Jyn Erso who motivated him to question his typical tactics and darkness.
Seeing as how this more noble transformation doesn't happen until Rogue One, viewers watching Andor should expect Cassian to remain a darker hero in this new prequel series. Likewise, he'll likely become more comfortable with killing now that he's about to a true cause fighting the Empire, rather than simply trying to survive and find his sister. As such, Andor's next face-to-face encounter with Syril Karn probably won't end with the same level of mercy.
Andor releases new episodes Wednesdays on Disney+.