The email arrived in 2016 from a sender identified only as “Alex” and offered James Landis the chance to cut the cost of his increasingly pricey drug habit.

A former Montgomery County deputy sheriff, Landis had been ordering bath salts off the internet for three years to help him sleep at night. But the cost of illegally shipping the banned substances from China was becoming prohibitive.

Intrigued, Landis responded. He had no idea, he would later claim, that a simple click of the reply button would transform him over the next year from a mere drug user into the linchpin of a global fentanyl trafficking conspiracy that U.S. authorities have linked to at least five deaths.

On Tuesday, federal prosecutors in Philadelphia unsealed indictments against three men in China who they say used the online moniker “Alex” to enlist Landis, 42, of East Norriton Township, as their primary distributor for synthetic opioids and other illegal drugs sold online and shipped into the United States.

It is unlikely that China will extradite the men — identified as Deyao Chen, Guichun Chen, and Liangtu Pan — to face prosecution here, U.S. Attorney William M. McSwain said at a news conference in Center City, in which he accused China of using drugs to “wage an undeclared war on America’s way of life.”

The case highlights China’s role in fueling the opioid crisis that has ravaged Pennsylvania and large swaths of the U.S.

Government studies have identified China as the leading source of fentanyl sold on the streets in Philadelphia and across the U.S. In just two years, more than $800 million worth of the deadly synthetic opioid was bought online and shipped from China to this country, according to a U.S. Senate report.

“The reach is global, spreading poison, misery, and death far and wide,” Montgomery County District Attorney Kevin R. Steele said at the news conference. “Because of traffickers like David Landis, people are dying across the Commonwealth of Pennsylvania and across the country from drugs that we are finding are too easy to get from China.”

Landis, a 10-year veteran of the Sheriff’s Office who left the job in 2014, pleaded guilty in a secret court proceeding last year.

He never met his suppliers. He never learned their real names. And yet, between 2016 and 2017, he shipped more than 2,900 parcels to users in 21 states and 19 countries — including Australia, Senegal, Japan, and Switzerland.

Their racket, as outlined in court filings, was brazenly simple. Rather than retreating to the dark web for online sales of illegal drugs, Landis’ suppliers sold their wares openly on English-language websites easily accessible around the world, investigators said.

Landis himself found them that way in 2013 while on the hunt for bath salts after seeing an ad for the substances on late-night TV. And it was through those sites that Landis allegedly first approached his suppliers for a way to cut down his shipping costs.

They quickly struck a deal. As orders came in, the Chinese suppliers allegedly packaged the drugs in boxes with innocuous labels such as “hair tonic,” “gift,” “cable,” and “electronic products,” then shipped them to a U-Haul storage facility Landis had rented in Roxborough.

There, Landis would repackage the contraband in mason jars and mail them to their intended destinations.

The arrangement helped the suppliers hide the source of the product, investigators said, and Landis was happy to help as long as they kept paying him with bitcoin and drugs.

In less than a year, Landis was paid the equivalent of more than $40,000 for his efforts, according to court filings.

U.S. Postal Service investigators uncovered the operation in 2017 after intercepting two first-class parcels containing fentanyl headed to Landis’ storage unit. Montgomery County authorities traced the unit to the former deputy.

And while Landis immediately admitted his guilt, he said he knew next to nothing about “Alex,” whom he believed to be a lone man sending him drugs.

Officials from the U.S. Attorney’s Office, the Montgomery County District Attorney’s Office, the Pennsylvania State Police, and Homeland Security Investigations declined to answer questions about how they traced “Alex” to the Chinese men charged in the indictment unsealed Tuesday, citing the sensitivity of their investigative techniques.

They focused instead on the damage their drug trafficking operation wrought.

Five customers in Georgia, Tennessee, Ohio, and Illinois died from overdoses within days of receiving orders shipped by Landis from East Norriton, McSwain said Tuesday.

As a result, Landis faces a mandatory minimum prison sentence of 20 years after his guilty plea in November to 63 counts, including charges of conspiracy and drug importation, possession, and distribution.

He has remained in federal custody since his 2017 arrest. His lawyer, Kenneth A. Young, did not return calls for comment Tuesday.

McSwain expressed doubt that Landis’ coconspirators would ever join him behind bars.

“Let’s be honest about what China is,” he said. “'The People’s Republic of China’ is an oxymoron if I ever heard one. It’s not a republic. It’s not for the people. It’s a dictatorship that does not respect the rule of law.

“We’re not expecting them to extradite these people into our hands, but there are good reasons to indict these people anyway and educate people about the dangers.”