SALT LAKE CITY >> The pills arrived in thousands of mailboxes across the country, round and blue, with the markings of pharmaceutical-grade oxycodone stamped into the surface.

Prosecutors would later call them “poison” — counterfeits containing fentanyl, a potent synthetic opioid that has written a deadly new chapter in the American opioid epidemic. They were shipped from the suburbs of Salt Lake city.

That’s where a clean-cut, 29-year-old college dropout named Aaron Shamo made himself a millionaire building a fentanyl trafficking empire with not much more than his computer and a few friends.

For three weeks this summer, those suburban millennials climbed onto the witness stand at his federal trial and offered an unprecedented window into how fentanyl bought and sold online has transformed the global drug trade. There was no testimony of gangland murders or anything that a wall at the southern border might stop. Shamo called himself a “white-collar drug dealer,” drew in co-workers from his time at eBay and peppered his messages to them with smiley-face emojis. His attorney called him a fool; his defense was that he isn’t smart enough to be a kingpin.

How he and his friends managed to flood the country with a half-million fake oxycodone pills reveals the ease with which fentanyl now moves around the world, threatening to expand the epidemic beyond America’s borders: Powder up to 100 times stronger than morphine was bought from a laboratory in China and arrived in Utah via international mail; it was shaped into perfect-looking replicas of oxycodone tablets in the press that thumped in Shamo’s basement and resold online. Then it was routed it back into the postal system in thousands of packages addressed to homes across this country awash with prescription painkiller addiction.

The largest civil litigation in history is testing how the pharmaceutical industry should be held accountable for inundating the country with billions of addictive pain pills, spreading mass addiction that led to this. Purdue Pharma, maker of the blockbuster drug OxyContin, reached a tentative $12 billion settlement this week with about half the states and roughly 2,000 local governments. A trial of other pharmaceutical companies is scheduled for next month, in which communities will contend that their mass marketing of prescription painkillers sparked an epidemic.

The crisis began in the 1990s, as prescription opioids paved the road to heroin, which led to fentanyl. It has killed tens of thousands of Americans since it appeared on the streets in 2013. There are two sources of supply. Mexican cartels and packages shipped direct from China, where it is produced in a huge and under-regulated chemical sector. There are many upstart dealers like Shamo, officials say. Seizure data shows trafficking quickly expanding worldwide. In 2013, four countries reported fentanyl seizures. By 2016: 16 countries.

It is so potent, so easy to transport, large-scale traffickers no longer require sophisticated networks, said Mike Vigil, former chief of international operations for the Drug Enforcement Administration. All they need is a mailbox, internet access and people with an appetite for opioids. And consumption rates are rising from Asia to Europe to Latin America as pharmaceutical companies promote painkillers abroad.

The profit margins for illegal fentanyl are irresistible. The DEA estimates a kilogram synthesized for a few thousand dollars could make a dealer more than $1 million.

“Any moron can basically become a major drug kingpin by dealing in fentanyl,” Vigil said. “You can have somebody with an IQ minus 100 who becomes an overnight multimillionaire.”

By the time a seized package heading from China to Utah led investigators to Shamo, he had already made at least 458,946 potentially poisonous pills, the government said. They found $1.2 million stuffed in his sock drawer and in a safe, plus more tied up in online cryptocurrencies.

Shamo built his drug-trafficking organization initially with his longtime friend Drew Crandall.

The pair began by selling Adderall, prescribed for attention deficit disorder, on the dark web — a wild, unregulated layer of the internet reached through a special browser. There are underground marketplaces where guns and drugs are traded and money is exchanged anonymously through cryptocurrencies. They expanded — peddling the club drug MDMA, magic mushrooms, date rape drugs, cocaine — all while barely having to leave the house. They bought a pill press and manufactured fake Xanax, the anti-anxiety medication.

Then a local drug dealer suggested to Shamo he’d make a fortune selling fake oxycodone made with fentanyl. Crandall left the country, and Shamo recruited another friend, Jonathan Luke Paz, to help him press oxycodone.

He sold pills both to individual users and drug dealers, who then sold the pills on the street. When police intercepted one single day’s shipment, it contained 34,828 fentanyl pills destined for homes in 26 states. Some were advertised on the dark web as fentanyl, but others weren’t, purporting instead to be 30 milligrams of oxycodone.

Federal prosecutors allege dozens of his customers died, though charged him only in connection with one death: 21-year-old Ruslan Klyuev, who died in his bedroom in Daly City, California, with the envelope that delivered the pills from Utah near his feet.

Shamo was convicted of 12 counts, including continuing criminal enterprise, the so-called “kingpin charge” that is typically reserved for drug lords like El Chapo and carries a mandatory life sentence. The jury deadlocked, though on the 13th count, the death of Klyuev.

But experts warn the fentanyl trade is rapidly expanding.

The day Shamo was convicted, a single dark web marketplace had thousands listings claiming to be oxycodone. There was no way to tell whether they originated in a pharmacy or somebody’s basement.

“Pharma-grade A++,” one listing promised. “24-hour shipping!”