BEIJING — Ms Yang Bin was at home when two dozen Chinese police surrounded her house and entered, searching for the man she had recently taken in as a houseguest. Filing in quickly, the officers found their suspect upstairs and arrested him, ending a weeks-long manhunt.

Police also detained Ms Yang for questioning. They wanted to know how Mr Xu Zhiyong, one of China’s most outspoken government critics, had come to find refuge with her, a Communist Party member and former government prosecutor.

For Ms Yang, the turn of events came with no small irony. In her old job, she had escorted death row prisoners to a police station near the one in which she was being interrogated, in the southern Chinese city of Guangzhou.

This time she was regarded as a suspect, and police had also taken her husband and 20-year-old son.

“Even though I was being questioned like a criminal, I knew in my heart I hadn’t done anything wrong,” Ms Yang, 50, who was later released with her family, said in a recent telephone interview from her home on Seagull Island, a rural area on the outskirts of Guangzhou.

“When many people look at the system, they see its strength. When I look at it, I see only its fragility.”

Ms Yang’s evolution from government prosecutor to defense lawyer with sympathies for pro-democracy activists is more than just an unusual career trajectory in China.

It embodies the disillusionment of those in the Communist Party establishment who have found the space for internal dissent shrinking rapidly amid the worst repression in recent years.

An insider in the Communist Party-controlled legal system, Ms Yang spent 23 years as a prosecutor in Guangzhou. She developed a fearsome reputation, racking up hundreds of convictions of murderers, thieves and drug dealers with clinical efficiency.

That experience has given her a deep understanding of the system’s flaws. The courts are sharply tilted in favour of police and prosecutors, and wrongful convictions are common.

She once believed in working within the party in the hope that economic progress would bring political openness and a fairer justice system. But when she tried to apply her ideals at work, she found herself sidelined and assigned a desk job.

That, to her, was proof that the party-controlled system could no longer tolerate even its most loyal critics.

Five years ago, she quit to become a defense lawyer, taking on cases that challenge powerful vested interests, such as defending farmers who were being thrown off their land by corrupt local officials.

Now her line of work has made her a target of authorities, who recently revoked her license. Defense lawyers in China often face harassment, disbarment, beatings and imprisonment for their work, particularly if they take on politically sensitive cases.

“In China, there is room for exceptional and compassionate people to change things in the system,” said Dr Jeremy L. Daum, a senior fellow at Yale Law School’s Paul Tsai China Center.

“But for some people there comes a moment when you start to believe that nothing you do can stop the worst of injustices.”

Since rising to power in 2012, China’s authoritarian leader, Mr Xi Jinping, has tightened control over the judiciary and waged a blistering campaign against rights lawyers and activists.

Some former establishment insiders have paid a heavy price for criticizing the government, including Ren Zhiqiang, a tycoon and decades-long Communist Party member who was sentenced to 18 years in prison in September after he criticised Mr Xi.

Ms Yang, the lawyer, said she used to describe herself as being with the party’s “reform faction,” a loose label for those who hoped for change to come from within the system. She paused and then laughed darkly.

“I guess you could say I belong to the ‘despair faction’ now,” she said.

Ms Yang first rose to national prominence in 2005 when she, as a prosecutor, made a surprising plea for leniency for Zhou Moying, an impoverished migrant worker convicted of drowning her baby.

Zhou, who was already struggling to raise three children, had killed her sick 8-month-old daughter in desperation because she could not pay for her medical treatment.

“We must not forget the people behind her who are struggling at the bottom of society,” Ms Yang said at the time. “This is the conscience that the law should have.”

The judge handed down a 10-year prison sentence, but Ms Yang helped Zhou find a lawyer to file an appeal, which led to a reduction of her sentence to six years. When Zhou was released from prison in 2011, many news outlets praised Yang for her unusual compassion.

“I realised that as a prosecutor I could — that I should — make an impact on individual lives,” Ms Yang recalled.

Growing up in a family of factory workers in a small town in Hunan province, she had rarely felt as empowered. After university, she moved to Guangdong province in 1992 where she later found work at a local county prosecutor’s office.

She began to handle criminal cases at the age of 28 and within several years was promoted to a position in the top prosecutors’ office in Guangzhou.

Despite the tight constraints of the job, Ms Yang looked for ways to push the boundaries.

In one case, she brought relatives of a homicide victim and the defendant together for reconciliation. In another, she tracked down the family of a man who she believed had been wrongfully convicted and offered to help them appeal the sentence.

Ms Yang was publicly praised for her empathy in the case of Zhou but said she faced resistance internally. In 2011, Ms Yang was pulled from the courtroom and reassigned to a desk job.

“I felt like I had lost my soul,” she said.

In 2015, Ms Yang quit. She yearned for the freedom to take on cases without political intervention.

As a defense lawyer, she successfully sued the Guangzhou Lawyers Association for requiring attorneys to prove that they had no criminal record before practicing, arguing that it placed an undue burden on lawyers.

She has also represented villagers in southwestern Yunnan province embroiled in a land dispute with local officials.

Her license to practice was recently revoked after the law firm she had worked for in Guangzhou refused to renew her contract last year, because, she thinks, of her advocacy on behalf of her clients.

Ms Yang said she planned to sue the government but was not optimistic.

Still, Ms Yang says she had no regrets about the path that she has chosen.

“The freedom I gained is freedom that would be unimaginable to those within the system,” Ms Yang said.

“Then again, freedom for Chinese people is always very limited.” THE NEW YORK TIMES