BETHLEHEM, Pa. (AP) — After his fiancee died taking drugs that came in the mail, a Florida man took investigators to the "dark web" store where he ordered them.

The investigation that unfolded over the next four months led federal agents to the door of a Bethlehem man who allegedly sold the substances that caused the woman's death.

Jeremy P. Achey's arrest last month on federal drug charges revealed a possible Lehigh Valley node in a global network of drug dealers moving the trade from the streets to a hidden part of the internet. He was one of 40,000 vendors, prosecutors say, in the dark web's largest marketplace, where users could anonymously buy illegal drugs, stolen credit card information, firearms and computer hacking tools before federal authorities, working with law enforcement around the world, seized it this month.

But other dark web bazaars exist and more are likely to spring up, presenting an ongoing challenge for authorities. The transactions are anonymous and difficult to trace and, law enforcement officials say, they're a more accessible source for fentanyl and similar powerful narcotics that are fueling the opioid overdose epidemic.

"It has opened up certain types of drugs to users who might not have been predisposed to use them," said Dusty Cladis of the U.S. Drug Enforcement Administration, noting that online sales eliminate the need to meet a dealer face-to-face and remove the fear of being arrested.

The potency of drugs such as fentanyl, up to 100 times stronger than morphine, means they can be distributed in small quantities that are easily mailed. That makes them available in places where drugs might have previously been hard to buy.

"It's going to college campuses and military bases — places where it might be hard for traditional hand-to-hand drug transactions to occur," Cladis said, adding that the locations include small communities that street dealers haven't reached.

Carnegie Mellon University researchers tracked purchases in 35 dark web marketplaces and estimated in 2015 that the markets had $300,000 to $700,000 in transactions every day.

Achey, 43, allegedly operated his store in a dark web marketplace called AlphaBay, which served more than 200,000 users before it suddenly and mysteriously winked out of existence July 4. On Thursday, the Justice Department announced an international operation to seize AlphaBay's servers and arrest its founder, Alexandre Cazes, a 25-year-old Canadian living in Thailand. AlphaBay's front page was replaced with the message, "This hidden site has been seized," beneath the seals of the Justice Department, FBI and DEA.

(At a hearing earlier this month, Achey's attorney argued that the government's evidence against Achey was deficient and that the charges should be dismissed. Federal public defender Catherine Henry said the packages were labeled "not for human or veterinary use" and "They can't prove at any time he had knowledge ... they were being used for human consumption.")

Cazes, who was charged with racketeering, conspiracy to distribute narcotics and other offenses, killed himself while in custody July 12, the Justice Department said. But prosecutors in California, where Cazes was charged, are pursuing the civil forfeiture of luxury vehicles, homes, a hotel and millions of dollars in virtual currency owned by Cazes and his wife.

The investigation linked alleged AlphaBay vendors, including Achey, with numerous fatal overdoses across the country, the Justice Department said in a news release about the Alpha Bay takedown. In addition to the Florida woman who died in February, the DEA is investigating whether another 19 overdose deaths are attributable to drugs purchased from Achey's store, court records say.

This month, a man who lives in Darby, Delaware County, was charged with distributing a controlled substance resulting in death in connection with two fatal overdoses in Portland, Oregon. Federal authorities say he imported 14 packages of suspected fentanyl from China and sold more than 7 kilograms — about 15 pounds — of the drug through an AlphaBay store for $284,000. Court documents say investigators believe Achey also received at least some drugs from a supplier in China.

Federal investigators say Achey sold drugs under the online alias ETIKING. University of Indiana criminology professor Bill Mackey said ETIKING's store was typical of thousands of dark net stores around the world.

It sold substances chemically similar to fentanyl, a powerful opioid painkiller; ecstasy, a popular party drug; LSD, a hallucinogen; and benzodiazepine, a commonly abused anti-anxiety medication, court documents allege.

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"It's going to college campuses and military bases — places where it might be hard for traditional hand-to-hand drug transactions to occur.

— Dusty Cladis, U.S. Drug Enforcement Administration

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The store's patrons paid only in bitcoin, an online currency tied to no government, that can be exchanged for U.S. dollars. The marketplace was accessible only through the Tor network, a system employing a special web browser that routes online traffic randomly through thousands of servers around the world to conceal the origin and destination of the data.

Tor, developed in the mid-1990s as a Navy project to transmit top-secret information, is designed to conceal the IP address — a device's unique internet identity — making it virtually impossible to trace.

That's good for anyone who doesn't want authorities spying on their online activities, Mackey said, noting Tor has been used by people in restrictive countries to read websites that are banned. It played an important role in the Arab Spring that led to the ouster of authoritarian regimes in several Middle Eastern countries. Sites where whistleblowers can sound an alarm about wrongdoing in corporations or government also employ the dark web.

But the anonymity Tor provides apparently attracted a criminal element.

Dark web drug markets resembling eBay or Amazon began in 2011 with the creation of Silk Road. Law enforcement seized Silk Road and arrested its operator, who went by the pseudonym "Dread Pirate Roberts," in 2013. He was sentenced to life in prison but competitors had already sprung up and incorporated the innovations that made Silk Road popular, Mackey said.

Like Silk Road, most anonymous online marketplaces now offer feedback from buyers about the quality of products and reliability of sellers. They also offer escrow services that release payments only when the product has been delivered. In that respect, online anonymous drug buying is safer than a face-to-face transaction, Mackey said.

"You're not subjecting yourself to violent crime. At the very worst you're going to be losing money," he said.

For law enforcement, however, dark web contraband trafficking evades a fundamental cyber crime investigative technique, said Jim Ponzi, a criminology professor at Regis University in Denver. Most online investigations into crimes involving child pornography or hacking succeed when police can identify an IP address, subpoena internet service providers for the subscriber's identity and trace it to a physical location.

Tor conceals that crucial clue, Ponzi said. And while software is continually being developed in an effort to defeat such privacy measures, the Tor network is constantly being improved to protect users' anonymity, he said.

"As fast as these things develop . you have people on the other side working to counter them," he said.

The most successful way to track people using the dark web is when they inadvertently or carelessly use their real identity in an online account connected with the dark web, Ponzi said.

That's what happened in Achey's case.

According to court documents:

After the Florida man whose fiancee fatally overdosed began cooperating with police, DEA agents used his AlphaBay account to make controlled purchases from the ETIKING dark web store. Each time, investigators received an envelope with a Houston return address containing drug analogues — chemicals similar to LSD and ecstasy.

Agents also met with a confidential source — the court documents don't say how he was located — who said he had done business with the owner of the ETIKING store. In fact, the source told agents, he had started ETIKING and sold the account for $400 along with 90 grams of fentanyl to a Pennsylvania man he knew only as Eric.

The source had saved some of the online messages he received from the ETIKING buyer that included information about his bitcoin account, the documents say.

Using grand jury subpoenas, agents discovered ETIKING used the same email address for his account with a company that printed mailing labels and sold postage online as he had with the bitcoin exchange he used in his dealings with the confidential source. He also listed his address on the bitcoin user agreement.

The last step of the investigation brought DEA agents and local police to stake out Achey's house, watching for two days as Achey and his wife, who is not charged, went to the post office to mail more than a dozen envelopes later found to bear the same Houston return address as that on the DEA's controlled purchases.

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Online:

http://bit.ly/2eGfydv

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Information from: The Morning Call, http://www.mcall.com