In late February, a man in South Carolina was accused of receiving more than three kilograms of fentanyl ordered on the dark net — or enough to kill 1.5 million adults, given that just two milligrams is a lethal dose.
A few weeks later in New Jersey, authorities arrested Chukwuemeka Okparaeke, who allegedly went by the screen name of Fentmaster on AlphaBay. He had received two kilograms of fentanyl from an address in Hong Kong, according to a criminal complaint.
Then in April, a Cleveland man, Alec Steinberger, 21, was arrested and accused of receiving a package of furanyl fentanyl that he was preparing to sell on the streets. He is said to have texted a 19-year-old who was helping him distribute the drugs to warn about their strength.
“Bro I did it last night any my pupils got so small they disappeared and then I was nodding for 18 hrs,” the text said, according to the indictment.
When the 19-year-old tried the drugs, he overdosed and died.
Mr. Okparaeke, Mr. Steinberger and Mr. Shamo have all pleaded not guilty. Lawyers for the men had no comment on their cases.
Law enforcement officials investigating these cases say that public documents underrepresent the number of cases involving the dark web because many court documents don’t mention the online sources of the drugs.
And many cases — including the death last year of the musician Prince from a fentanyl overdose — are still being investigated because of the relatively recent advent of the phenomenon.
“It has come to play a key role in the overdose crisis,” said Tim Plancon, who oversees the Drug Enforcement Administration in Kentucky, Michigan and Ohio, states at the epicenter of the overdose crisis. “It’s expanded beyond just your traditional drug smuggling and trafficking. There is just a lot more involved with it when you are dealing with folks on the dark web with virtual currencies.”
The United States is not the only country dealing with an influx of mail-order synthetic opioids. Canada and several European countries have also made recent arrests of suspects accused of being major online drug dealers responsible for multiple deaths.
But the numbers are particularly staggering in America. In 2015, the last year for which national data is available, fentanyl and similar drugs killed 9,580 people, or 73 percent more than 2014. The number of deaths rose even faster last year in areas that have released figures, such as Ohio and New Hampshire. Over all, deaths from drug overdoses are soaring in the United States, and most likely exceeded 59,000 last year.
Authorities say that most of the illicit supply of synthetic opioids is produced in labs in Asia and especially China, where many of the precursor chemicals are either legal or easier to procure.
Latin American drug cartels are also getting synthetic opioids from Asia and moving them into the United States. But the operational ease of sending the drugs through the mail gives the method obvious appeal for Chinese producers, many of whom are technologically skilled enough to set up their own dark web shops.
One of the most frequently reviewed vendors of synthetic opioids on AlphaBay goes by the screen name BenzoChems. The vendor has shared online videos of his operations in China.
In a series of messages exchanged on AlphaBay’s internal messaging system, BenzoChems, who declined to provide his real name, said he had found that routing packages through Hong Kong, and then through the United States Postal Service, was the most efficient method of transit.
Some Chinese producers also list synthetic opioids for sale on websites on the ordinary internet, without requiring users to navigate to them through a special dark web browser. But most of the recent criminal complaints in the United States appear to involve drugs procured through markets that exist only on the dark web.
BenzoChems said that he had sold his products on ordinary websites, but those sites were quickly shut down by the authorities.
Dark web technology was originally developed by American intelligence agencies to allow for encrypted communication. News organizations, including The New York Times, use it to receive story tips from vulnerable sources.
But the illicit markets enabled by the dark web have made stopping the flow of deadly drugs much more complicated than it was when the authorities were trying to stop earlier waves of drug overdoses.
“We could give you a pretty good idea of the drug traffickers in town who can order kilos from Mexico — that’s a known commodity,” said Joseph M. Pinjuh, the chief of the organized crime task force in the United States attorney’s office in Cleveland. “What’s harder to track is the person ordering this from his grandmother’s basement.”
Lawmakers have tried to attack the problem by introducing legislation in Congress that would tighten the requirements on information gathered by the Postal Service. Last month, at a Senate hearing on the problem, Postal Service officials said they were working to collect information on more packages coming from China.
In recent months, though, the number of listings for fentanyl on AlphaBay and other dark web sites has been rising steadily.
Ms. Haun, the former federal prosecutor in San Francisco, said the tools that enabled dark web commerce made it very unlikely that the expanding traffic would be curtailed anytime soon.
“It’s only going to increase, and increase the types of communities and markets that might not have had as easy access to it before,” she said.