User blog comment:Emperor Maximus/On the Civil War/@comment-50.159.28.95-20150406214248/@comment-1600847-20150407190821

According to the few sources we have of the incident (The Bear of Markarth and dialogue with the Silver-Bloods), Ulfric had already retaken the city by the time the Legion arrived, and he was approached by Jarl Igmund, not the Empire itself. I'm sure the Empire didn't mind that he killed all the Reachmen, but it was Igmund who asked.