The investigation has asked a court to extend the arrest of Ukrainian pilot Nadia Savchenko, whom Russia has accused of complicity in the killing of Russian journalists, until September 10.

Investigator Timofey Grachyov said in motivating the request at the Moscow City Court on Wednesday that Savchenko's arrest needs to be extended so that she and her defense team could have enough time to study the case materials, after which the case should be forwarded to the Prosecutor General's Office, and then, if the latter draws up an indictment, be passed to courts.

"The lawyers have not started familiarizing themselves with the case," Grachyov said. "Savchenko has read 28 volumes of the criminal case," the investigator said, adding that the investigation was especially complicated as witnesses were based in various regions, and a lot of expert studies were ordered.

One of Savchenko's defense lawyers had told Interfax earlier that the case included 35 volumes.