Klebnikov, who was the editor of the Russian edition of "Forbes" magazine, was shot dead in Moscow in July 2004.
Two suspects, both ethnic Chechens, were accused of killing Klebnikov. A third Chechen was accused of complicity. Prosecutors argued Klebnikov was killed on the orders of another Chechen, allegedly as revenge for a critical book written by Klebnikov.
All three defendants originally pleaded not guilty. Critics of the trial said prosecutors failed to follow other lines of investigation. Klebnikov had reported on corruption and a range of murky business dealings.
The Supreme Court was acting on an appeal by prosecutors.
(compiled from agency reports)