The investigation of the murder of opposition Russian politician Boris Nemtsov has contract killing as its main version, TASS reported on Monday.

The news agency quoted an investigator as saying to the Moscow Basmanny District Court in that the search for the organizers and the person who had placed a contract on Nemtsov’s life was in progress.

While the probe is proceeding along all lines of inquiry, contract killing is the main suspicion, the investigator said.

Meanwhile, Khamzat Bakhayev, a suspect in the Nemtsov murder case pleaded not guilty during hearings at Basmanny Court on Monday.

The Moscow City Court on 1 April upheld the arrest of Anzor Gubashev, another suspect charged with involvement in the murder of Nemtsov but said the arrest of a further three suspects is unlawful and sent the issue for revision to the Basmanny Court.

Three out of a total of five suspects held in the case — Tamerlan Eskerkhanov, Khamzat Bakhayev and Shadid Gubashev — are to be kept in custody until the district court reviews the city court’s motion, presumably by 8 April.

The main suspect in the case, Zaur Dadayev, will remain in police custody until 28 April. On 1 April he pleaded not guilty to charges of murder and withdrew his earlier confession, saying he had spoken to investigators under duress.

Investigators think that Dadayev was the killer, while brothers Anzor and Shadid Gubashev, Khamzat Bakhayev and Tamerlan Eskerkhanov acted as his accomplices.

The five suspects have all been charged with premeditated murder committed by a group of individuals as well as illegal acquisition and possession of weapons. They face jail terms of up to 20 years or even life if convicted.