Under the PRC Criminal Law and Civil Code, what is the legal liability if a taxi driver discovers a high-value diamond necklace left in the car, intentionally conceals it, and refuses to return it to the verified owner upon demand?

1. No legal liability because items left in the car automatically become driver property
2. Civil liability for tortious restitution, administrative taxi license deduction/revocation, and criminal liability for the crime of embezzlement/conversion (侵占罪) if the value meets statutory thresholds
3. A minor administrative warning with no requirement to return the necklace
4. The passenger must pay the driver a salvage award equal to twice the necklace's value