Answer: Fingerprints are not conclusive evidence on their own.
Step-by-step explanation:
The thief could have worn gloves and those fingerprints could belong to the owners. If the fingerprints don't match those of the owners', you would still need more evidence to prove that those belong to the killer, such as their whereabouts at the time the vase was stolen, motive, etc. Fingerprints are not conclusive evidence on their own.