In Rogue One, Captain Cassian Andor is assigned a mission to kill Empire Science officer Galen Erso. With Galen in his sights he hesitates to kill Galen. Why?
We know Cassian is a Rebel and has no qualms about killing people, even if they aren't Stormtroopers. In the scene pictured below, when he meets with a Rebel informant (on his side) he kills him, presumably to protect information.
So why does his conscience perk up with the assassination of Galen Erso, who is indirectly responsible for the destruction of Jedha City which he witnessed first hand?