Well they did. Fritz worked the bolt to eject the remaining bullet and did so without testing the bolt action for fingerprints. Plus he didn't take photos of the rifle in situ.
Are you claiming investigators manhandled the Carcano to an extent that would leave it covered in fingerprints? Are you suggesting that latent, usable prints are easy to find and difficult to remove?
In regards Fritz, are you sure that immediately disarming (so-to-speak) any given firearm shouldn't be considered top-of-mind in
any circumstance, let alone a suspected murder weapon?