The court thereby rejected an appeal by Frenkel's lawyer against his detention.
Central Bank Deputy Chairman Kozlov, 41, was killed in Moscow in mid-September of last year.
Police later detained entrepreneur Liana Askerova on suspicion of being an accomplice in the Kozlov murder case, and she gave testimony implicating Frenkel, which was believed by Frenkel's defense to be the only evidence prosecutors had against their client.
In all, seven people have so far been detained in connection with the murder of Kozlov, widely described in the media as an honest official who led a crusade against money laundering and other criminal banking practices. Some of them have reportedly confessed to having been hired to kill the official.
Frenkel, 35, was arrested January 15. His defense said the arrest was illegal.
He published two letters following his arrest accusing the Central Bank of accepting bribes for allowing banks to join the deposit insurance system. Prosecutors are investigating Frenkel's accusations.
