Actually, I think it is islamic women that have been specifically trained (and brainwashed) for this assignment thus the light caliber rifle, the cunning, the cold-bloodedness of it.
Another thing, everyone is assuming that they are leaving the scene as soon as the shot is fired. I don't think they are. I think they're hunkering down, well-hidden and then once the heat is off (24-48 hours or so), they are then picked up by their comrades. Everything else is a ploy to throw off LE.
IMHO, this is war and it needs to be treated as such. It takes a sniper to catch a sniper...unfortunately, we appear to refuse to acknowledge that and remain "unarmed".
We know that the weapon is the same.
We do NOT know that the shooter is the same and it looks like a relay, the weapon changing hands for a one week period.