Forensic tests indicate that a former Chechen police official, now under arrest, is the man who shot dead Russian opposition leader Boris Nemtsov.
Russia's Interfax news agency has quoted a source in law enforcement authorities. But the source says the perpetrator could only be confirmed when the murder weapon is found.
The Chechen ex-policeman, Zaur Dadayev, with another man, has been charged by Russian authorities. They are among five men, all ethnic Chechens, now in custody. Dadayev has confessed to involvement in the crime.
Interfax said investigators are pursuing the line that the killing may have been motivated by Nemtsov's controversial remarks about Islam. Investigators have also identified foreign contacts of the suspects, and are investigating phone records.