The FBI is investigating the circumstances of late Indianapolis Colts owner Jim Irsay's death and the addiction recovery specialist who treated Irsay in his final days, according to a report from the Washington Post.

On Jan. 22, the Post reported that it reviewed a federal grand jury subpoena showing that the FBI requested "records and information relating to Irsay's death, his 'substance (illegal and prescription) use,' and his 'relationship with Dr. Harry Haroutunian,'" an addiction recovery specialist based in southern California.

Federal agents traveled to Indianapolis "for several days" in January to interview people who were close to Irsay, according to two people the Post cited with knowledge of the agency's investigation. Those people remained anonymous as they were not authorized to publicly discuss the ongoing investigation.

INDYSTAR: Death of Colts owner Jim Irsay being investigated by FBI, per report

The late Colts owner died at 65 last May while vacationing in Beverley Hills. At the time of Irsay's death, Haroutunian was staying at the same hotel "and overseeing Irsay's treatment," according to the Post.