The men always wore masks, Tursunay Ziawudun said, even though there was no pandemic then.
They wore suits, she said, not police uniforms.
Sometime after midnight, they came to the cells to select the women they wanted and took them down the corridor to a "black room", where there were no surveillance cameras.
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First-hand accounts from inside the internment camps are rare, but several former detainees and a guard have told the BBC they experienced or saw evidence of an organised system of mass rape, sexual abuse and torture.
Tursunay Ziawudun, who fled Xinjiang after her release and is now in the US, said women were removed from the cells "every night" and raped by one or more masked Chinese men. She said she was tortured and later gang-raped on three occasions, each time by two or three men.
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Internal documents from the Kunes county justice system from 2017 and 2018, provided to the BBC by Adrian Zenz, a leading expert on China's policies in Xinjiang, detail planning and spending for "transformation through education" of "key groups" - a common euphemism in China for the indoctrination of the Uighurs. In one Kunes document, the "education" process is described as "washing brains, cleansing hearts, strengthening righteousness and eliminating evil".
The BBC also interviewed a Kazakh woman from Xinjiang who was detained for 18 months in the camp system, who said she was forced to strip Uighur women naked and handcuff them, before leaving them alone with Chinese men. Afterwards, she cleaned the rooms, she said.
"My job was to remove their clothes above the waist and handcuff them so they cannot move," said Gulzira Auelkhan, crossing her wrists behind her head to demonstrate. "Then I would leave the women in the room and a man would enter - some Chinese man from outside or policeman. I sat silently next to the door, and when the man left the room I took the woman for a shower."
The Chinese men "would pay money to have their pick of the prettiest young inmates", she said.
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The Uighurs are a mostly Muslim Turkic minority group that number about 11 million in Xinjiang in north-western China. The region borders Kazakhstan and is also home to ethnic Kazakhs. Ziawudun, who is 42, is Uighur. Her husband is a Kazakh.
The couple returned to Xinjiang in late 2016 after a five-year stay in Kazakhstan, and were interrogated on arrival and had their passports confiscated, Ziawudun said. A few months later, she was told by police to attend a meeting alongside other Uighurs and Kazakhs and the group was rounded up and detained.
Her first stint in detention was comparatively easy, she said, with decent food and access to her phone. After a month she developed stomach ulcers and was released. Her husband's passport was returned and he went back to Kazakhstan to work, but authorities kept Ziawudun's, trapping her in Xinjiang. Reports suggest China has purposefully kept behind and interned relatives to discourage those who leave from speaking out. On 9 March 2018, with her husband still in Kazakhstan, Ziawudun was instructed to report to a local police station, she said. She was told she needed "more education".
According to her account, Ziawudun was transported back to the same facility as her previous detention, in Kunes county, but the site had been significantly developed, she said. Buses were lined up outside offloading new detainees "non-stop".
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Then sometime in May 2018 - "I don't remember the exact date, because you don't remember the dates inside there" - Ziawudun and a cellmate, a woman in her twenties, were taken out at night and presented to a Chinese man in a mask, she said. Her cellmate was taken into a separate room.
"As soon as she went inside she started screaming," Ziawudun said. "I don't know how to explain to you, I thought they were torturing her. I never thought about them raping."
The woman who had brought them from the cells told the men about Ziawudun's recent bleeding.
"After the woman spoke about my condition, the Chinese man swore at her. The man with the mask said 'Take her to the dark room'.
"The woman took me to the room next to where the other girl had been taken in. They had an electric stick, I didn't know what it was, and it was pushed inside my genital tract, torturing me with an electric shock."
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Alongside cells, another central feature of the camps is classrooms. Teachers have been drafted in to "re-educate" the detainees - a process activists say is designed to strip the Uighurs and other minorities of their culture, language and religion, and indoctrinate them into mainstream Chinese culture.
Qelbinur Sedik, an Uzbek woman from Xinjiang, was among the Chinese language teachers brought into the camps and coerced into giving lessons to the detainees. Sedik has since fled China and spoken publicly about her experience.
The women's camp was "tightly controlled", Sedik told the BBC. But she heard stories, she said - signs and rumours of rape. One day, Sedik cautiously approached a Chinese camp policewoman she knew.
"I asked her, 'I have been hearing some terrible stories about rape, do you know about it?' She said we should talk in the courtyard during lunch.
"So I went to the courtyard, where there were not many cameras. She said, 'Yes, the rape has become a culture. It is gang rape and the Chinese police not only rape them but also electrocute them. They are subject to horrific torture.'"
That night Sedik didn't sleep at all, she said. "I was thinking about my daughter who was studying abroad and I cried all night."
In separate testimony to the Uyghur Human Rights Project, Sedik said she heard about an electrified stick being inserted into women to torture them - echoing the experience Ziawudun described.
There were "four kinds of electric shock", Sedik said - "the chair, the glove, the helmet, and anal rape with a stick".
"The screams echoed throughout the building," she said. "I could hear them during lunch and sometimes when I was in class."
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Another teacher forced to work in the camps, Sayragul Sauytbay, told the BBC that "rape was common" and the guards "picked the girls and young women they wanted and took them away".
She described witnessing a harrowing public gang rape of a woman of just 20 or 21, who was brought before about 100 other detainees to make a forced confession.
"After that, in front of everyone, the police took turns to rape her," Sauytbay said.
"While carrying out this test, they watched people closely and picked out anyone who resisted, clenched their fists, closed their eyes, or looked away, and took them for punishment."
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Detainees had food withheld for infractions such as failing to accurately memorise passages from books about Xi Jinping, according to a former camp guard who spoke to the BBC via video link from a country outside China.
"Once we were taking the people arrested into the concentration camp, and I saw everyone being forced to memorise those books. They sit for hours trying to memorise the text, everyone had a book in their hands," he said.
Those who failed tests were forced to wear three different colours of clothing based on whether they had failed one, two, or three times, he said, and subjected to different levels of punishment accordingly, including food deprivation and beatings.
"I entered those camps. I took detainees into those camps," he said. "I saw those sick, miserable people. They definitely experienced various types of torture. I am sure about that."
It was not possible to independently verify the guard's testimony but he provided documents that appeared to corroborate a period of employment at a known camp. He agreed to speak on condition of anonymity.
The guard said he did not know anything about rape in the cell areas. Asked if the camp guards used electrocution, he said: "Yes. They do. They use those electrocuting instruments." After being tortured, detainees were forced to make confessions to a variety of perceived offences, according to the guard. "I have those confessions in my heart," he said.
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President Xi looms large over the camps. His image and slogans adorn the walls; he is a focus of the programme of "re-education". Xi is the overall architect of the policy against the Uighurs, said Charles Parton, a former British diplomat in China and now senior associate fellow at the Royal United Services Institute.
"It is very centralised and it goes to the very top," Parton said. "There is absolutely no doubt whatsoever that this is Xi Jinping's policy."
It was unlikely that Xi or other top party officials would have directed or authorised rape or torture, Parton said, but they would "certainly be aware of it".
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For a while after her release, before she could flee, Ziawudun waited in Xinjiang. She saw others who had been churned through the system and released. She saw the effect the policy was having on her people. The birth rate in Xinjiang has plummeted in the past few years, according to independent research - an effect analysts have described as "demographic genocide".
Many in the community had turned to alcohol, Ziawudun said. Several times, she saw her former cellmate collapsed on the street - the young woman who was removed from the cell with her that first night, who she heard screaming in an adjacent room. The woman had been consumed by addiction, Ziawudun said. She was "like someone who simply existed, otherwise she was dead, completely finished by the rapes".
"They say people are released, but in my opinion everyone who leaves the camps is finished."
And that, she said, was the plan. The surveillance, the internment, the indoctrination, the dehumanisation, the sterilisation, the torture, the rape.
"Their goal is to destroy everyone," she said. "And everybody knows it."