XINGTAI, China — Chinese authorities publicly sentenced a man to death and imprisoned eight others Thursday for trafficking fentanyl to the United States, after a joint investigation by law enforcement agencies in the two countries.

The rare case of cooperation comes amid concern in the U.S. and criticism from President Donald Trump that China is not doing enough to stop the flow of illicit fentanyl, which is blamed for rampant addiction and thousands of deaths.

“Honestly, I think this is a complicated issue,” Yu Haibin, deputy director of China’s National Narcotics Control Commission said in an interview with NBC News. “The huge demand in the U.S. and the supervision of the drug over the counter should be the main factor.”

The case started with an arrest in New Orleans in August 2017 that revealed information about a woman in China, known as “Diana”, who sold narcotics online and shipped orders to the U.S. That information was passed on by American officials to drug investigators in China, who spent months uncovering a sprawling network of fentanyl labs, producers and dealers.

When a large wire transfer was made to “Diana,” authorities moved in and made “an extraordinary number of arrests and seizures”, according to Austin Moore, an Immigration and Customs Enforcement official working at the U.S. Embassy in Beijing. The raids netted about 26 pounds of fentanyl, as well as substantial amounts of related opioids, along with information that was shared with the Department of Homeland Security.

“More than 50 U.S. residents and addresses attempted to obtain fentanyl from the Diana organization,” said Moore, who attended the sentencing in Xingtai along with other American officials. Those details launched over 25 new cases in the U.S., resulting in 3 major arrests in New York and Oregon.

Chinese officials were eager to showcase the collaborative effort and its success at a time when China-U.S. relations are strained over trade and accusations of Chinese complacency on fentanyl. Journalists were invited to Xingtai, about 220 miles from Beijing, to observe the court proceedings and attend a news conference at a nearby hotel. It was highly organized, including a police escort for shuttle buses.

The nine defendants — five men and four women — were led into a courtroom and seated in black chairs. They did not speak. One of three presiding judges read out details of the case, the charges against them and their sentences. The man considered the ringleader, Liu Yong, was described as leading a conspiracy to defy Chinese laws to manufacture and smuggle fentanyl to the U.S. He was given a two-year reprieve on his death sentence.

“Their measures are very covert,” Liu Zhiyong, the deputy chief of Xingtai Public Security Bureau told NBC News. “Our investigators lack chemistry expertise … it’s definitely hard to identify and verify this type of substance.”

The smuggling ring was shut down in November 2017, but Chinese officials insisted the timing of the sentencing and news conference was tied solely to the court process, and was not related to a pending "phase one" China-U.S. trade deal.

Officials noted there are two more joint China-U.S. fentanyl investigations ongoing.