ByZachary Folk,

Forbes Staff.

The FBI is investigating the death of billionaire Jim Irsay, the owner of the Indianapolis Colts who died last May, the Washington Post reported citing a grand jury subpoena, and looking into a doctor who reportedly treated him before his death with pain medicine and ketamine.

Federal investigators are examining Irsay’s drug use and his “relationship with Dr. Harry Haroutunian,” a California-based addiction doctor, the Post reported citing a federal grand jury subpoena and people familiar with the investigation.

Irsay, who struggled with addiction years earlier, which led to a 2014 arrest for drunk driving and drug possession, died “peacefully in his sleep” last May at age 65, his family said in a statement at the time.