When I listened to the rest area defense program; I never heard any mention of being aware of multiple offenders. It would always be better to "assume" that there are multiple offenders, rather than get blind sided by the other guy in the shadows.
Predator and prey roles can work both ways.
If you have to explain why you threatened or used deadly force, you have to be able to articulate elements of what you were sensing/thinking/doing. Saying simply that it seemed a good idea at the time will not cut it, unless your name is Rooster Cogburn.