Two Russian cosmonauts have used knives and shears to cut samples from around a hole in the Soyuz spacecraft, which Moscow says may have been caused by a drill.
Roscosmos space agency says it wants to find out whether the 2mm puncture was made on Earth or in space.
It has ruled out a manufacturing defect and says it may have been deliberate sabotage, but Nasa has played down such speculation.
The “small but dangerous” hole found in the Soyuz MS-09 craft, docked with the International Space Station, has now been sealed.
An oxygen leak was stopped and air pressure was stabilised, though the three US astronauts, two Russian cosmonauts and one German were never said to have been in danger.
Oleg Kononenko and Sergey Prokopyev’s spacewalk was described as “unprecedented in its complexity”.