According to an investigation, Russian opposition politician Boris Nemtsov was followed for almost a year by an agent linked to a political assassination team before being shot dead.
President Vladimir Putin had a bitter rival in Nemtsov. His assassination in 2015 was the most high-profile political assassination since Putin took power.
Before his murder, Bellingcat, The Insider, and the BBC discovered evidence that Nemtsov was followed on 13 trips.
Boris Nemtsov rose to prominence in the 1990s, serving as President Boris Yeltsin’s deputy prime minister and being widely tipped as Yeltsin’s successor.
Instead, Mr. Putin rose to power, pushing Mr. Nemtsov to the periphery of Russian politics. He rose to prominence as a campaigner, exposing corruption and denouncing Russia’s 2014 invasion of eastern Ukraine.
Mr Nemtsov was shot dead just yards from the Kremlin on February 27, 2015, just days before he was set to lead a protest against the war.
For his murder, five Chechen men were quickly apprehended and imprisoned. However, the official investigation failed to answer the most pressing questions: who ordered the killing and why?
Seven years later, the BBC, in collaboration with the investigative websites Bellingcat and The Insider, can reveal evidence that Nemtsov was being followed across Russia by a government agent linked to a secret assassination squad in the months leading up to his death.
Mr Nemtsov was followed on at least 13 journeys, according to the investigation, which was based on leaked train and flight reservation data.
Mr Nemtsov was last followed by the agent on February 17, 2015, just 10 days before his assassination.
Valery Sukharev is the agent’s name, according to his documents. All evidence indicates that he was a member of Russia’s main security agency at the time. One of the FSB’s responsibilities is to manage internal political threats on behalf of the Kremlin, which includes tracking people’s movements across the country.
The FSB’s Magistral database keeps track of all flight and train reservations. However, the database can be used to reveal not only the movements of people Russian agents might want to track, but also the movements of the agents themselves, such as Mr Sukharev.
Bellingcat acquired some of the original data for this investigation through Russian brokers. The data was obtained by the brokers from corrupt officials with access to Magistral. The BBC also used information that was freely given to us by sources with access to copies of Magistral.
The data from Magistral has previously been used by Bellingcat to investigate assassination attempts in Russia. Their investigations revealed evidence of a secret hit squad operating within the FSB, which has targeted Kremlin foes. These allegations have always been refuted by the Russian government.