Legal Question in Criminal Law in California

They can only look in places where the stolen items could be. For instance, police searching for drugs could look in a lot more places than officers trying to find a stolen grand piano.

They are not required to look the other way if they run across obvious contraband while they are searching. For example, if they are searching for weapons and find drugs, they can seize the drugs.

This is called the "plain view" doctrine.

One of the main U.S. Supreme Court cases on this topic is Arizona v. Hicks (1987) 480 U.S. 321. Police officers investigating a shooting noticed some expensive stereo equipment and suspected it might be stolen. They moved the equipment around so they could see the serial numbers, then checked to see if it was stolen, which is was. The court said turning the equipment around was an illegal search, and suppressed the evidence.

Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like Avvo, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.