Authorities in Beijing have criminally detained Guo Yushan, an activist legal scholar who was instrumental in the escape of dissident Chen Guangcheng, pictured here in Washington in September. Agence France-Presse/Getty Images

BEIJING—Authorities in Beijing have criminally detained an activist legal scholar who was instrumental in the escape of dissident Chen Guangcheng two years ago, his lawyer and family said, in the latest move in a sustained clampdown on legal activists.

A dozen or so police and state security officers took Guo Yushan from his home in a Beijing suburb early Thursday morning, his wife Pan Haixia said Sunday. “They came in with a warrant and took a lot of things as evidence, his computer, his iPhone, iPad and some hard drives,” Ms. Pan said.

The detention notice later given to the family said that he had been detained on suspicion of “picking quarrels” — a crime used in the prosecution of dozens of activists in recent years, according to a copy of the notice his lawyers posted online Saturday. The lawyers said they submitted an application to the Beijing No. 1 Detention Center to meet with Mr. Guo, but had yet to get a response.

A person answering the phone at the detention center on Sunday he had no information about the case. Beijing’s Public Security Bureau didn’t immediately respond to a faxed request for comment.

China’s Communist Party later this month is set to convene an annual policy conclave, and such meetings are often preceded by security sweeps against activists like Mr. Guo. This year’s Central Committee meeting will focus on reforming the legal system, particularly the judiciary, according to state media and legal scholars. But it also comes amid a more than yearlong effort by authorities to rein in outspoken activists and while the Chinese leadership is dealing with protests for free elections in Hong Kong.

Authorities recently detained a number of artists who had expressed public support for pro-democracy protests, though activist friends said they hadn’t seen Mr. Guo issue any public statements on Hong Kong.

“It’s become clear that the door of ’picking quarrels’ is open for everyone. It means they can go after him, not just for what he may have been doing recently, but for everything he’s done in the past,” said Hu Jia, a prominent activist and friend of Mr. Guo’s.

Mr. Guo is a co-founder of the Transition Institute, an independent think tank in Beijing that advocates political and economic liberalization. In 2012, he was one of a small group of activists that coordinated the daring escape of Chen Guangcheng, the blind legal activist who was being held under house arrest in the eastern province of Shandong. Mr. Chen made it into the U.S. embassy in Beijing, sparking a diplomatic crisis that was resolved after then-Secretary of State Hillary Clinton negotiated a deal to allow him to travel to the U.S.

Since then, Mr. Guo has kept a low profile. The scholar agreed to leave the Transition Institute when authorities threatened to shut it down last year, close friends and diplomats said. According to a European diplomat, Mr. Guo has also limited his contact with foreign embassies since aiding Mr. Chen’s escape.

“He’s been very, very low key,” said Mr. Hu.

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