Not exactly. Very few tires and boots leave no marks at all, while a number of firearms leave no marks when cycling unfired ammunition. That is the difference - ALL spent casings will show distinctive marks from the chamber, extractor and ejector, because when fired the expansion of gasses swell the casing and the force of ejection is much greater. Plus you have the impression of the firing pin on the primer.
Even with fired rounds, comvictions have been tossed out based on the concerns raised by this exact evidence on appeal. Honestly, the best statement that should be made is "consistant with". It is more like fiber evidence, truly.
I really am expecting LE to come up with a lot more evidence: DNA, fingerprints, souvenirs from RA's home, etc so that less solid things and shaky witness testimony won't even come into play.
And maybe KAK will testify against him, who knows.
But you're welcome to disagree!
JMHO