Need some help from the team!

I got a character that needs a name. It seems SOMEONE is assassinating prominent Separatists who have since made nice with the Empire. No one knows who or why, but there rumors of this XXXXXXX killer have made their ways to the ears of our protagonist, who is a Separatist who has made nice with the Empire.

What's this killer's name? I have no idea. The Zodiac Killer? The Scarlet Pimpernel? The Ice Dagger? What do people call him?

Maybe he leaves a calling card, or kills in a particularly unusual method, and either of these lead to his name. This is going to be a little background plot, possibly paying off in the future.

Any ideas?