Ken,
The problem with Luger serial numbers is that there are duplicates. The serial number would include the letter suffix stamped under the SN on the front of the frame.
If the SN of the so-called stolen Luger is not the same including the letter suffix, manufacturer (DWM, Erfurt, Mauser, Simson,etc.) of the same year of production, it cannot be proven to be the same Luger. The first 10,000 Lugers of any given year will not have a letter suffix.
To prove that this is the "stolen" Luger,
1. Same SN including letter suffix.
2. Be the same year of production.
Stamped with date 1910 thru 1918 Imperial WWI Lugers.
Stamped 1920-1921 for Weimar Lugers.
Stamped K (1934 code), G (1935 code), 1936 thru 1940, as well as "41" or "42" for Mauser WWII Lugers.
3. Be the same manufacturer.
DWM, Erfurt (WWI), Simson late 1920s. Mauser 1934 thru '42.
If all of these markings along with SN + suffix don't match the stolen Luger. It cannot be proven to be the same Luger.
The SN alone is not sufficient to prove it's the same one.
Get an exact description including all dates and markings, if possible, of the stolen Luger. If everything doesn't match exactly, it's not the same one.
If the collector is a dedicated and Honest Luger collector? He will know the difference, and will know how his was dated , marked, etc. And should be able to provide this information.
If the Police go solely on the SN as proof? They are aiding and abetting in the theft of your Luger by letting him have it.
You can go to this site and see how many different variations, makers, dates and markings there are.
http://www.simpsonltd.com/index.php?...fd1a13e68b086c
Ron