No one aboard the space station was in significant danger as a result of the leak, which was detected last Wednesday evening by flight controllers.
The crew first addressed the problem by applying tape to the hole, according to NASA, and later, Russian flight engineer Sergey Prokopyev plugged the hole using gauze and epoxy, a super-strong sealant.
A Russian cosmonautics expert, Alexander Zheleznyakov, was extremely skeptical of theories that the hole was drilled deliberately from space.
"Why should any of the crew try to do that? I would not like to use the word nonsense, but all this does not fit in well with logic," Zheleznyakov told TASS.
He offered another possibility: "Most probably all had happened at the manufacturer's plant. A hole that has been patched up with glue is hard to detect. ... Most probably, a worker drilled a wrong hole and then patched it up and then either avoided telling anyone or those he had informed preferred to keep quiet, too."
The Soyuz spacecraft was made by the Russian corporation Energia, according to TASS. The International Space Station is currently hosting three NASA astronauts, two Russian cosmonauts and one European Space Agency astronaut.
John Logsdon, a space policy expert at George Washington University, told NPR that there is "a kind of generalized concern about the decline of quality control in Russian space industry in recent years." If the hole was accidental, he said, "and then covered up and nobody inspected and found it ... that's troubling."
Roscosmos has appointed a commission to investigate and expects its work to be done by mid-September.
Leroy Chiao, former commander of the International Space Station, told NPR that he finds it somewhat mysterious that the hole appears to be hand-drilled through the material that's about half an inch thick. "It would take a little while to drill all the way through the hole," he said.
Chiao recalled how the astronauts were vigilant during his expedition about anything that might cause a drop in pressure, like this leak did. "Pressure dips are certainly not a routine thing," he said.
"So as soon as we hear a noise, we would rush over to the very sensitive pressure gauge to make sure that the pressure was holding," Chiao said. "That was definitely something that we were attuned to."
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