In January last year Miao Guofang, with whom Zhang spent the most time during her stay in Illinois, paid her last tribute to the dear friend lost, before she left the US permanently to take up a teaching post in a Chinese university. In freezing cold, Miao tied a golden bell to a tree standing where Yingying was before she got into that car.

"Guofang and I have a lot in common...both of us confront problems head-on,"Zhang wrote in her diary."But I may compromise, I may want to be famous..."

In the summer of 2018, while waiting at home in China for the trial to begin, Ye Lifeng joined a local Christian church."Why must my daughter die? I asked myself and everyone I knew. Now I leave this question to God."

In October last year Zhang Xinyang married and had a son, whom his parents are helping him take care of. "For them, the newborn may have provided some rare respite, but the pain inevitably comes back," says Zhang, who holds on to his sister's letters and diaries for consolation.

"Yingying is always present through her absence."

Barely two months after Hou returned to China last year he began his two-year stay in a village school tucked deep in the mountain wrinkles in Guangdong province, not far away from Zhang's hometown in neighboring Fujian province.

"Both Yingying and I had volunteered to teach during our holiday breaks at university, but we never got a chance to do it for as long as we would have wished," says Hou, who has taken with him several notebooks filled with Zhang's neat handwriting, notes taken by her in preparation for her studies in the US.

"None of the rules supposed to be followed by a small-town girl worked for Yingying. She was curious, fearless and relentless in her quest for knowledge－the making of a true academic."

The overwhelming majority of Hou's students are children left behind by their migrant-worker parents. Struggling with negligence and sometimes the insensitivity of adults around, many are in various states of mental anguish, some suffering from depression.

"What I had been through gave me the ability not only to sympathize, but to empathize with them," Hou says. "They make me aware that despite the hard carapace that has taken shape over me as result of what had happened, I'm still soft at heart."

In Chinese class, students from higher grades wrote poems revealing their tender adolescent love. For music class, Hou played guitar.

"Yingying loves music," Hou told an audience who were out for Zhang in the concert one day before Christensen was arrested."I wrote many songs for her, and this is her favorite: Dream Like A Child."

On that hot summer day in Beijing in 2018, after showing Shi the place where Zhang had lived, Hou was about to leave. As he was walking away, Hou heard a thumping sound, and looked back to see a bird, seized by apparent pain, flapping and thrashing itself on the pavement in a futile effort to fly.

"I don't know where the bird came from－it seemed that she had dropped from somewhere quite high and had severely injured herself," says Hou, who, under Shi's camera, stooped down and put his hand gently over the little creature.

The bird soon became quiet. When Hou lifted his hand moments later, the bird's life was gone.

Hou put the bird into the small hole he had dug out on the grassy ground with a stone chip, covered it with dirt, smoothed the earth, and then they left. Nothing seemed to have happened.

"I wasn't thinking much at that moment," Hou says."But as I was watching the movie, it became so clear that it was Yingying. She came to say goodbye, and to give me what I'd always wanted a proper burial for her."