The source, who was familiar with the investigation, said authorities were still trying to determine a possible motive for the apparent attack and did not have any suspects.
Lesin, who was President Vladimir Putin's press minister from 1999 to 2004 and once headed state-controlled Gazprom-Media, was found unconscious on Nov. 5 on the floor of his room in the Doyle Washington Hotel, also known as the Dupont Circle Hotel.
An autopsy concluded Lesin had died of blunt force injuries to the head. He also suffered blunt force injuries to the neck, torso, arms and legs, the U.S. capital's Office of the Chief Medical Examiner and the Metropolitan Police Department said in a brief statement on Thursday.
Shortly after Lesin was found, Russia's RT television cited family members as saying he had died of a heart attack.
Police who first investigated the hotel room where Lesin's body was found did not find any damage or evidence indicating foul play, a law enforcement source said on Thursday.
The police department said in a statement on Friday it was continuing to actively investigate Lesin's death.
A Russian Embassy spokesman said Russian officials have been pressing for information on the death through diplomatic channels for several months. He said the Russians expected an explanation from the American side following Thursday's autopsy report.
ABC News has said Lesin had been accused of censoring Russia's independent media. He became head of Gazprom-Media Holding in 2013 but resigned the following year.
(Reporting by Mark Hosenball; Editing by Tim Ahmann and Bernadette Baum)