Umm no, not obviously an assualt rifle. Lots of .223 hunting rifles, could have been a mini 14.
.223 is not a military caliber.
Yes our ban is rather pointless and tough, it prevents legit gunowners from buying some interesting things. I can't speak for criminals, I don't beleive they consult the laws before driving to NH.
This is all speculation at this point, we have no information what weapon was used other than the caliber.