I have a Thompson Model 1928 SMG that's not mine, but it's sitting in the safe at the shop, waiting to be transferred to a customer.
It was built by Colt, and shipped (with a 100-round drum) to Peter von Frantziuz, a gun dealer in Chicago, well known to provide guns to the gangsters of the era. He then sold it to Frank V. Thompson, who bought guns for the mafia. The gun was sold for $200, with an extra $25 charge for the 100-rnd drum, and a $4 charge to have3 the gunsmith remove the serial numbers on the gun and drum. To cover-up the sale of the gun, it was recorded as having been shipped to another person, in Elgin, IL. The box shipped to Elgin actually contained a brick for weight.
Thompson then sold the gun to a Joe Howard, of Detroit. It is speculated that Howard was really an alias for some gangster, but that's not confirmed. That's where the paper trail ends, until 1968.
In November 1968, a Model 1928 Thompson was amnesty registered by Arthur Godfrey, originally from Detroit, MI, who had joined the Secre Service in 1951. Godfrey started out in Detroit, but was eventually transferred to Washington, DC. Godfrey served as the Deputy Special Agent in Charge, Presidential Protection Detail. On the morning JFK was assasinated, Godfrey had worked the midnight to 8 am shift. At the time of the assassination, Godfrey was in Austin, waiting for the President to arrive later that day.
At some point, both the gun and the drum that I have were parkerized, most likely by the FBI Gun Vault. This indicates the possibility that the gun was used at some point by either FBI or Secret Service Agents in the line of duty. (It is known that Secret Service Agents used a Thompson during another Presidential assassination attempt, against President Truman.)
When Godfrey passed away in 2002, his gun collection was sold. The gentleman who bought the Thompson recognized that the serial number wasn't original. Nor did it appear to be an amnesty registration serial number, as those usually began "IRS" and this one begins "XO." He sought out the assistance of a renowned Thompson historian, and they pulled the barrel off of the gun, where a serial number was found. That serial number matched the one sold to von Frantzius in the '20's.
How it came into Godfrey's possession is unknown. It's interesting that the gun was owned by both reputed gangsters and by a man charged with protecting the President of the United States. The gun has seen use by both sides of the law. Now, that's a history.