You hear a door slam and footsteps running away from you. When you wake up a bit more, you see that the would-be assassin has gone only a very short distance. Highlighted by a distant flame, he is cowering in terror. "Don't you kill ol' Jim!" he pleads. "I'm just the lowest ring of the Defias Brotherhood, man! I can tell you anythin' you want! The Hill's all up in flames now, there's nowhere to run..." He devolves into incoherent mumbling.
Just kill him. Your priority here is to protect Lou. Find out what Jimb knows.