Legally owning a handgun - unkown source

[Standard]

Hypothetically, say someone got a handgun given to them by someone other than a family member a while back. We have to assume it was through less than legal means,as there was no paperwork done. This person has no idea as to the origin of the handgun, if it's stolen, been used in a crime, etc. This person wants to keep the handgun, but doesn't know how to legally do so.
What would be his or her next step?
I know this sounds trite, but it really is a hypothetical.

[Oldnoob]

Hypothetical answering, that someone can self register to once own name by submit in this form to DOJ

http://ag.ca.gov/firearms/forms/pdf/volreg.pdf

Only cost $19.
If the firearm turn out to be registered "missing" than that someone should do the right thing and cooperate with law enforcement for necessary actions.

[leelaw]

It depends. If the transfer was before 1991, then it could very well be legal. If it's more recent, then you've got an issue and it'd be best to contact an attorney.