Drama in the Mansion

Imagine an enormous mansion, filled with 10 families. All of the families get along, except one pair, who often dispute. Last night, and argument became serious, and ended in gunshot. However, the victim was unharmed, so the charge became attempted murder. Despite this, the police were still called to the seen to take the criminal into custody. The issue was, neither the victim, nor the criminal, would disclose their role in the shooting. The police are dumbfounded, so the call in their best detective. That's where you come in. You place the families in a line, as shown below. You know that the families have the dispute are the ones involved in the shooting. After lining them all up, you immediately realize who the guilty family is.

(NOTE: the families were able it choose where in line they stood, as long as they stayed together)

How did you know which families were involved?