I don't think Muhamad is the sniper. I think Muhamad is either working with him, or know who he is.
Moose said he was not the sniper. So, Greta said the same.
Had a thought though. Perhaps they have someone in custody already? What ever happened with the second vehicle they were looking for after the rifle was pointed at the school bus?
Maybe they did get someone, but there is a second person involved? The person Moose is addressing is the second person. The sniper is caught like a duck in a noose. It's important that you hear this... because this means the sniper/partner is out of commision, so the second person may as well turn themself in, or carry on alone, I guess.
I kind of wonder if John Mohammad and the step son ARE the shooters. Mohammad with military background = head shots. The 16 year old step son, the abdominal shots???
Maybe after the media blabbed about saying 'persons of interest' just to get to talk to LE... Moose may have been forced to issue warrants and forget about 'persons of interest' ploy?
Anyway, just theorizing.