MOSCOW - The International Space Station (ISS) crew that landed in Kazakhstan on Thursday brought back a dust filter from the Soyuz MS-09 spacecraft, which is currently docked to the ISS and where, in late August, the station's crew found an air leak, as part of the investigation into the incident, a source in the space industry told Sputnik on Sunday.

On August 30, the ISS crew detected an air leak caused by a microfracture on a wall of the orbital module of the Soyuz MS-09 spacecraft, which had docked to the ISS on June 8. The hole was sealed by the crew on the same day. Russia's state space corporation Roscosmos set up a special commission to investigate the incident. Earlier in October, Roscosmos head Dmitry Rogozin said that the commission had concluded that a manufacturing defect was not the cause of the incident.

"Among the cargo brought back by the Soyuz MS-08 spacecraft, item 111 attracts the most interest. It is the dust filter from Soyuz MS-09 spacecraft and swabs taken from and around the hole," the source said.

The source added that experts would try to find traces of aluminum, which is what the module is made of, and if they did find it, it would prove that the hole appeared when the module was already in orbit.

The Russian Central Military District said later in the day that the Soyuz MS-08 had been delivered to Moscow and would be handed over to Russia’s rocket and space corporation Energia.

In early September, a source from the space industry told Sputnik that Russian cosmonauts at the ISS had been asked to collect all evidence that could help to shed light on what could have caused the hole to appear.

On November 15, the ISS crew are set for a spacewalk during which they will examine the hole from outside before the Soyuz MS-09 spacecraft departs from the ISS in December. It will be impossible to examine the hole upon the return of the spacecraft to the Earth because the orbital module separates from the descent module, in which the crew lands, and burns when entering into the atmosphere.