This story has been updated with comment from volunteers behind a GitHub page.

A group of volunteers in China who worked to prevent digital records of the coronavirus outbreak from being scrubbed by censors are now targets of a crackdown.

Cai Wei, a Beijing-based man who participated in one such project on GitHub, the software development website, was arrested together with his girlfriend by Beijing police on April 19. The couple were accused of “picking quarrels and provoking trouble,” a commonly used charge against dissidents in China, according to Chen Kun, the brother of Chen Mei, another volunteer involved with the project. Chen Mei has been missing since that same day. On April 24, the couple’s families received a police notice that informed them of the charge, and said the two have been put under “residential surveillance at a designated place.” There is still no information about Chen Mei, said his brother.

It is unclear whether the arrest of the couple and the disappearance of Chen are directly linked to their GitHub project, named “Terminus2049.” The Beijing police could not be reached for comment.

The project, named after a planet in Isaac Asimov’s series Foundation, has been preserving censored news stories, videos, and articles from individuals shared on messaging apps like WeChat since January 2018. The purpose of the project was to “encourage the public to resist ‘404,’” referring to the error message displayed when a webpage has been deleted or banned by authorities, according to a 2018 post (link in Chinese) on Terminus2049.

During the outbreak, the project shifted its focus to storing articles including a Chinese magazine’s interview (link in Chinese) with Wuhan doctor Ai Fen, who said she was the first to reveal the existence of the epidemic but who was later reprimanded. The article, first published in March, was taken down within hours of publication, spurring a race among internet users who used various creative ways, including coded language and emojis, to keep the article alive. Terminus2049 also preserved a strongly worded critique (link in Chinese) aimed at Chinese leader Xi Jinping penned by outspoken professor Xu Zhangrun. In the essay, Xu attacked Beijing’s social controls and censorship. He was later reportedly placed under house arrest and his account has been suspended on WeChat.

Chinese citizens had been turning to Microsoft-owned GitHub after the outbreak began, as it remains one of the few major foreign websites that can still be accessed in China. Now, volunteers linked to these GitHub pages are facing the growing risk of reprisals from authorities. Another GitHub page, #2020 nCov memory, which was initiated by seven volunteers around the world to chronicle personal accounts and news stories of the outbreak, is no longer publicly available. The team behind #2020 nCov memory said in an email to Quartz that they will suspend operation of the page and collection of submissions due to the “situation” in China, and that they hope to see “sunshine tomorrow.”

In addition to the GitHub volunteers, three journalists have also disappeared since February while reporting from Wuhan, the city where the outbreak was first discovered. Among them, only Li Zehua, a former employee of the state broadcaster, recently resurfaced, and said in a video that he had been detained and placed under quarantine by police for “disrupting public order,” but also praised the actions of the police. The whereabouts of citizen journalists Chen Qiushi and Fan Bin remain unknown.