Do you think the ATF could identify the original owner?
Pre 1968 GCA firearms are pretty much invisible. But once the 4473 and bound book requirements came in, the ATF can go to the manufacturer and find out where the gun was originally shipped (distributor, shop) and then find the original purchaser in the bound book. After than the trail can grow cold, but the newer the weapon, the more likely they can follow it.
CA DOJ can list every handgun you ever bought or sold in CA. Of course this assumes all sales went thru an FFL. They started this same program for long guns Jan 2014.
You cannot buy a handgun from another state without the transfer taking place at an FFL in the buyers state (Fed law). If you move to CA and bring guns, you will have to register them.