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When the Department of Justice announced the first-ever indictments of two Chinese nationals accused of shipping massive amounts of fentanyl through the mail to customers in the United States, it was major news. Flanked by top law enforcement officials, Deputy Attorney General Rod Rosenstein touted the cases at an October press conference as a "milestone in our battle to stop deadly fentanyl from entering the United States."

But when Rosenstein was asked whether the two alleged kingpins, Xiaobing Yan and Jian Zhang, were in custody, he declined to comment. VICE News found out why: Chinese authorities have so far declined to apprehend the men, with one top official claiming that the U.S. overstepped its authority and failed to provide enough evidence to justify their arrest.

Speaking exclusively to VICE News in Beijing, Yu Haibin, director of precursor chemical control at the National Narcotics Control Commission, the Chinese equivalent of the DEA, said the fentanyl cases remain under investigation. But, he added, “the U.S. unilateral indictment of Chinese people has made our investigation difficult.”

“China does not have solid evidence to show that they have violated Chinese law”

“China does not have solid evidence to show that they have violated Chinese law,” Yu said. “Our American counterparts haven't provided such evidence either. Therefore, we have not reached a point to indict or arrest these two suspects.”

Asked about Yu’s remarks, Justice Department spokeswoman Nicole Navas said, “the Chinese government has played a supportive role with this investigation, and continues to do so.” Navas declined to comment further “in order not to compromise ongoing investigations and prosecution efforts.”

DEA spokesman Rusty Payne said the indictments of the two Chinese nationals “speak for themselves.”

“We want these individuals brought to justice in the United States,” Payne said, “and we will continue to go after other major manufacturers and distributors of dangerous, deadly fentanyls throughout the world.”

There’s no extradition treaty between the U.S. and China, so it’s unlikely the men would stand trial in American courts even if they were arrested.

“We want these individuals brought to justice in the United States”

Yan, 40, was indicted in a Mississippi federal court on nine total counts related to illicit drug manufacturing and distribution. The Justice Department says he operated at least two plants in China that were “capable of producing ton quantities of fentanyl and fentanyl analogues.” Yan also allegedly “monitored legislation in the United States and China,” and tweaked the formulas of his drugs to skirt the law, supplying at least 100 dealers across the U.S.

Zhang, 38, was indicted in federal court in North Dakota on an array of drug and money laundering charges. The Justice Department says he “ran an organization that manufactured fentanyl in at least four known labs in China and advertised and sold fentanyl to U.S. customers over the Internet.” Zhang allegedly supplied pill presses and other supplies to manufacture counterfeit painkillers, along with “many thousands” of fentanyl packages, including one shipment that led to a fatal overdose.

According to data released Thursday by the CDC, opioid overdoses killed about 42,000 Americans last year, and fentanyl was the leading cause. Fentanyl and other powerful synthetic opioids caused about 19,000 deaths in 2016, more than double the number in 2015.

The DEA says most of the fentanyl comes from China, with traffickers sending the product through the mail directly to customers in the U.S. or supplying Mexican cartels, which cut the fentanyl into heroin.

President Donald Trump raised the issue of fentanyl during his visit to Beijing in November, telling reporters that he and President Xi Jinping “discussed ways we can enhance coordination to better counter the deadly drug trade,” and agreed to place “a special emphasis” on fentanyl. Earlier in the year, Chinese authorities responded to U.S. pressure and banned production of several fentanyl analogues, including the elephant tranquilizer carfentanil, which was linked to a spate of overdose deaths.

Yu acknowledged that some illicit fentanyl continues to come from his country, but said “we don’t have evidence or data to support the the case that it’s almost all from China alone.” He also blamed the “growing demand” for fentanyl among U.S. users, and said the opioid problem is “strongly connected” to state-level marijuana legalization.

“Many states in the U.S. are still working on legalizing marijuana, trends like this certainly encourages fentanyl-type substance abuse,” Yu said. “We hope the U.S. could strengthen collaboration instead of placing blame on one region.”