[Uncle Chip]

I didn’t know that snipers worked in groups.

[ThunderSleeps]

I would hope that extractor marks, firing pin indent characteristics, and possibly fingerprints on the shell casings would indicate if this were one shooter who changed positions several times or multiple shooters. 19 minutes is plenty of time to shoot, move, shoot with pre-planned and scouted positions...

I would lean towards a single shooter myself. If you're going to do something criminal and stupid the chances of getting caught go up exponentially with the number of people in on it. The fact that they haven't gotten a line on this means it is either a small group of extremely well disciplined people or more likely just one whack-job that knows how to keep his mouth shut.