MOSCOW (AP) - A former Russian security service officer who investigated whether security agents were connected to a series of deadly apartment bombings was denied parole, Russian news agencies reported Wednesday, six months after he was abruptly re-arrested.

The case against Mikhail Trepashkin has raised questions about the independence of the Russian judiciary and prolonged doubts about the official version of the 1999 bombings, which killed about 300 people in Moscow and two other Russian cities. Some Kremlin critics alleged they were staged by authorities as a pretext for launching the current Chechen war.

Trepashkin was released in August after serving just under half of a four-year sentence for revealing state secrets. But a regional court later overturned a lower court's decision releasing him on good behavior.

Interfax and RIA-Novosti said Wednesday the court in the Ural Mountain region of Sverdlovsk upheld a district court ruling that denied parole to Trepashkin. Defense lawyer Lyubov Kosik said she would appeal the denial. The Federal Security Service, the main KGB successor agency where Trepashkin worked until 1997, alleged that he was recruited by the British agents to collect compromising materials on the explosions with the aim of discrediting the Russian security agency.

He was arrested in October 2003.