Chinese student Zhang Yingying. (File photo: Xinhua)

Chinese police made a significant contribution to investigating the murder in the US of visiting Chinese scholar Zhang Yingying, the victim's family lawyer said Wednesday, citing it as a successful example of close cooperation between Chinese and US police.

Eight videos taken in China, including seven interviews with Zhang's schoolmates and teacher, have been played since Monday at the penalty hearing for Brendt Christensen, who is charged with kidnapping and murdering Zhang, Zhang's family attorney Wang Zhidong, told the Global Times on Wednesday. 

The videos were filmed by a joint work team comprised of officers from China and the US, said Wang. 

Upon the application by the FBI and US Department of Justice, China's Ministry of Public Security invited US personnel to China to investigate Zhang's case. 

Led by the ministry's criminal investigation bureau, the team was formed in October of two US federal prosecutors, three FBI agents, an interpreter, an FBI Beijing office chief from the US side and Chinese officers from the ministry's international and criminal investigation bureaus, Wang said. 

The team went to Beijing, Shanghai, Zhang's undergraduate university in South China's Guangdong Province and her hometown in East China's Fujian Province to obtain evidence, which was photographed and translated as court evidence for the penalty phase.

"Four US personnel in the work team became key witnesses in the penalty hearing. That cooperation has been kept a secret until today," Wang said. 

The penalty phase will decide if Christensen faces the death penalty or serves a life sentence.

Three language specialists who worked with the FBI and two FBI agents, along with Zhang's father, brother and boyfriend also testified. A video of Zhang's mother was played at court, said Wang.

The family "were heartbroken, but this is the moment they have been fighting for in the past two years to seek justice for Zhang," Wang said.  

Zhang was reported missing on June 9, 2017. Her remains have not been found, but prosecutors said her DNA was matched to blood later found in three spots inside Christensen's bedroom.

Christensen was found guilty of her abduction and murder in June after two years of investigation.