They have yet to confirm a genetic match, the source added.
An Embraer executive jet on which Prigozhin was listed as a passenger crashed in Tver region north of Moscow on Aug 23, according to Russia’s Federal Air Transport Agency.
Six other passengers were listed along with a crew of three, including pilot Alexei Levshin.
A source close to the situation, who spoke on condition of anonymity due to the sensitivity of the matter, said investigators had told Levshin’s family that they had “documentary proof” he had been on the crashed plane.
Levshin’s family are due to undergo a DNA test later on Friday to establish that they are his relatives, the source said.
Investigators did not mention the fate of others registered as being on board the flight, the source said.
(Reporting by Filipp Lebedev, editing by Guy Faulconbridge and Angus MacSwan)