Thank you all for your informative replies. It is a contemporary story. Basically, the private eye (the protagonist in my novels) disarms an intruder who tries to kill him. The intruder escapes, but the private eye retains the gun and notices that the serial number on the barrel has been obliterated. However, when he removes the grip, he finds the serial number that was stamped on the frame. This serial number allows him to trace the handgun to its original owner (not the intruder)--- a key aspect of the plot.
Hope this explains why I needed this information. Any and all comments are welcome. I appreciate your help.
JPOD
How is he able to trace the handgun to the original owner?
In real life, the ATF can trace a firearm from the manufacturer to the distributer and then to the retail outlet and the first retail purchaser. It's an involved process though as most of the paperwork is not electronic and paper records have to be hand searched. This is especially true of older paperwork.
(And each step has to be done. The manufacturer would have no idea where it went after it went to the distributer, and then the distributer's records have to be searched to find the retailer, and then the retailer's records have to be searched to find the buyer).
Local law enforcement agencies can request the ATF do this, but normally would have no reason to do so. If the ATF did do this at the request of a local agency it would take a couple months, minimum, for trace to work through the process.
There is no way for a PI to have access to this kind of trace. There is no centralized database he could access, or even hack into, to get the info. And, it's not as simple as "asking for a favor" from a police friend or even a ATF agent. The whole trace process is cumbersome and requires official paperwork and effort on the part of many people.
I do have a workable alternative for you though. For quite a well it was popular for firearms owners to electro pencil their name or other ID on their guns for proof of ownership in case of theft. Because this was kind of ugly, it would often be done under the grips.
In some cases people would add their Social Security number as well (this was before worries of identity theft).
The PI could disarm the bad guy and, when he checks under the grips, find the original owners name and possibly even soc sec or old phone number or driver's license number. (I've seen all three used as ID on guns before).
Of course, this only works if the bad guy stole or "borrowed" the gun from the original owner. If the original owner gave the bad guy the gun specifically to kill the PI, then the original owner obviously wouldn't give the bad guy a gun to use that had the owner's name electopenciled on the gun.
This avoids the whole "impossible for the PI to trace the gun" problem.
EDIT: I forgot to include the possibility of a state level registration system that the PI could get access to, probably unofficially. If the state the story takes place has handgun registration, that is a possibility, and would be more likely then a ATF trace.