Boston Man Pleads Guilty to Possession of Machinegun (DOJ)

BOSTON - A Boston man pleaded guilty today in federal court in Boston to unlawful possession of a machinegun.

James Thelwell-Mullen, 32, pleaded guilty to one count of unlawful possession of a machinegun before U.S. District Court Judge Allison D. Burroughs who scheduled sentencing for July 29, 2025. In July 2024, Thelwell-Mullen was indicted by a federal grand jury.

On or around April 28, 2023, Thelwell-Mullen unlawfully possessed a machinegun conversion device, commonly referred to as a "Glock switch" - a device designed to enable a Glock semi-automatic pistol to fire automatically. According to court documents, a machinegun conversion device, as well as two privately made firearms, ammunition, firearm magazines, other firearm accessories, and one plastic bag of fentanyl, were recovered during a search of Thelwell-Mullen's Boston residence. Messages on Thelwell-Mullen's phone indicated that he was also selling machinegun conversion devices.

The charging statute provides for a sentence of up to 10 years in prison, three years of supervised release and a fine of up to $250,000. Sentences are imposed by a federal district court judge based upon the U.S. Sentencing Guidelines and other statutory factors.

United States Attorney Leah B. Foley; James M. Ferguson, Special Agent in Charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives, Boston Field Division; and Boston Police Commissioner Michael Cox made the announcement today. The case is being prosecuted by Assistant U.S. Attorney Elianna J. Nuzum of the Criminal Division.