McMillan's family had launched a campaign to find their loved one.
Police said he disappeared April 23 from his home in Southeast Washington after heading out for a date with a woman he had met on the Internet. Relatives found his car, police said, and his bank cards had been used after his disappearance.
The human remains were found Oct. 30 along the Suitland Parkway. Authorities this month identified them as McMillan, and ruled the death a homicide on Tuesday.
No arrest has been made.