basically , anyone can buy parts to build a gun generally would run between $ 400 and $ 1,200 , according to websites advertising the parts and edwards ' own estimates .
an investigation determined that bertics had secretly purchased various parts for the guns by mail and then built the weapons himself , edwards said .
according to edwards , everything bertics did to assemble the gun was legal .
lower receivers normally require serial numbers .
police have not said bertics ' motive in showing up at the ortons ' door .
he and orton dated for a while but had not seen each other in that capacity since 2013 , edwards said .
police quickly focused the investigation on where bertics got the two guns found at the scene .
advertisement small aspects of the crime still were being investigated , according walnut creek murder - suicide suspect used “ ghost guns , ” police lt .