One more thing... IF the original owner filed an insurance claim on this gun and was paid for it, then the insurance company owns it now.
They may be very willing to let you keep the gun if you pay them for whatever amount that they paid out on it. Which may be much less than the $500.
Insurance companies do not want the hassle of owning and reselling property.
And especially if it is firearms. They don't want the paperwork and liability.
You may be cut a very good deal on it.
Try and do a little background investigation on your own or through the police at the originating agency (police department where the gun was reported stolen in the first place)
Good luck to you.