MOSCOW, March 28 (Xinhua) -- A Russian Federal Security Service officer (FSB) was involved in the murder of journalist Anna Politkovskaya, Russian news agencies reported on Friday.

    Formal charges of involvement in the murder of Politkovskaya have been brought against FSB officer Lieutenant-Colonel Pavel Ryaguzov, a representative of the Russian Prosecutor-General's Office said on Friday.

    "Nine persons, including Ryaguzov, have been held responsible" on charges of grave crimes. "The case has some complexity," as two other criminal cases against Ryaguzov add to it, the Itar-Tass news agency quoted the prosecutor as saying.

    The identity of a killer of Politkovskaya has been established and Ryaguzov is being searched for, the prosecutor official said.

    The investigation of the criminal case on the murder of Politkovskaya has been extended to September 7, a state prosecutor said at a sitting of the Moscow military district court, at which the extension of arrest of Ryaguzov was reviewed.

    Earlier media reports said Ryaguzov was suspected of informing killers of Politkovskaya about her address in Moscow.

    "In September of 2006, Ryaguzov ascertained the place of residence of Politkovskaya at the request of certain Shamil Burayev and passed this information to him," a source was quoted by the Itar-Tass news agency as saying. Ryaguzov was detained in August 2007.

    Politkovskaya, a reviewer with Novaya Gazeta, was shot to death on October 7, 2006, in the entrance lobby of a house on Lesnay Street where she rented an apartment. Investigators spotted a criminal group led by a Chechen that "specialized" on contract murders.

    The investigation also ascertained that former officers of the Russian Interior Ministry and security services provided information to killers.