A Keene man in federal custody died Friday afternoon at the Strafford County jail, according to the U.S. Marshals Service.

Addison Southwick, 30, was being held at the jail in Dover on a federal drug charge.

Chief Deputy U.S. Marshal Brenda Mikelson this morning confirmed Southwick’s death. She declined to release further details, including how Southwick died, because her office and the Strafford County Sheriff’s Office are still investigating.

Keene police and U.S. Homeland Security Investigations arrested Southwick on June 19, after receiving information that he traveled regularly to Lawrence, Mass., to pick up heroin and crack cocaine to sell in the Keene area, according to an affidavit filed in federal court.

Law enforcement officers found about 140 grams of suspected heroin or fentanyl and about 2 ounces of suspected crack cocaine in Southwick’s vehicle, according to the affidavit, written by a Homeland Security Investigations agent.

Southwick appeared in U.S. District Court in Concord the next day, charged with possession with intent to distribute.

A hearing had been set for July 11 to review his detention status.

Paul Cuno-Booth can be reached at 352-1234, extension 1409, or pbooth@keenesentinel.com. Follow him on Twitter @PCunoBoothKS.