hmm... if you have found a firearm out and about then you should take it to thenearest copshop to have the serial number checked.
No way to answer. Sorry.
Yes.
what gun are we talking about here
First, the general public does not have access to the NCIC database of stolen firearms. Second, without more information, we cannot even state what kind of gun that is. A serial number is not unique to only one gun in the world. Your local law enforcement officers may be able to help, but they will want to have the gun in hand when checking it (in case it IS stolen)
No practical way to do this. If the seller was a dealer, and you filled out paperwork at the show, you may be able to go to the dealer and have them check their records. If you do not know who the dealer was, no way.
There is no easy way for a private citizen to check the legitamacy of a given firearm. The stolen gun database (NCIC) is a Federal computer system open only to law enforcement. MOST states do NOT have a system nor a requirement to register guns. Local law enforcement MAY be willing to run your gun through the NCIC system, but will want to have possession of the gun in case it IS stolen.
There is no practical way for a private citizen to do this- but dealing with a licensed gun dealer is a good way to go. Information, such as serial numbers of stolen firearms, etc, are on a database that is not available to a non-police officer.
Contact your local police department and give them the serial number. The Police can check on the stolen gun list maintained by the BATFE. If the gun is stolen, the Police will conficate the piece and begin investigation of how it was acquired.
Contact the police.
Expect the police to expect YOU to explain how you came to possess a gun that had been stolen- just like any other property.
Robber trap.
Depends on the DA.