Sadulayev said Russian authorities "treacherously" killed Maskhadov, having invited him to "talks" and guaranteed his security "at the highest level."
Sadulayev, who is in hiding, made the accusation on March 8 in a statement posted on a Chechen pro-separatist website, kavkazcenter.com.
Maskhadov was killed by Russian forces on March 8, 2005, in a village north of Grozny. Russia said at the time he was killed "during an operation led by FSB [security service] special forces."
Maskhadov headed the Chechen separatist forces during the 1994-96 war. He was elected Chechen president in January 1997.
He was one of the most wanted men in Russia, with Moscow blaming him for a string of deadly attacks on civilian and military targets in Russia.