I think they did similar when they found unidentified prints on the sliding door (an entry/exit point) in VD's house, but since it wasn't DW's, it doesn't seem too significant to them. It's tough to know what else they don't look into if Feldman doesn't know and wouldn't therefore bring it out.
...and on the bannister at the top of the stairs...and on the desk in Danielle's bedroom... DID THEY COMPARE THESE UNIDENTIFIED PRINTS to see if they matched?