The source said that the suspects were engaged in debt collection-related activities in Moscow. Their meetings took place in a well-known Moscow restaurant, where security staff decided to launch audio and video surveillance of suspicious customers.
After the murder of Boris Nemtsov, the undercover agent, who was close to suspected Chechen debt collectors, advised police to confiscate the video footage from the restaurant and use it in order to identify and detain the suspects, according to the source.
It also said that the footage particularly helped to detain Tamerlane Eskerhanov, Shadid Gubashev and Khamzat Bakhayev.
Meanwhile, Russian Investigative Committee spokesman Vladimir Markin has denied information about the suspects being detained with the help of an undercover agent. He declined to elaborate.
A total of five people have been arrested in connection with the killing of Boris Nemtsov. Apart from Eskerhanov, Bakhayev and Gubashev, they include Zaur Dadayev and Shadid Gubashev's brother Anzor.
Investigators believe that the killer is Zaur Dadayev and that the rest could be his accomplices.