Hartley why do you think there were no more prints on the rifle? And surely as crime scene photos they worthless if the gun had been moved around
The crime scene photographs are most certainly not useless.
Obviously we are all guessing as to why there are not more identifiable prints on the rifle.
It may be the case that the surfaces of the rifle simply do not lend themselves to receiving prints, thus the failure to identify many of them.
Alternatively, the rifle could have been wiped down, the killer may have worn gloves, or the police may not have sufficiently preserved the evidence.