For its two and a half years online, thousands of drug dealers sold every kind of narcotic imaginable on the anonymous online marketplace known as the Silk Road. But put one of the site's heroin dealers in a courtroom and ask him questions under oath, and the scale and consequences of that drug empire suddenly seem much more real.

Today at the trial of Ross Ulbricht, the 30-year-old Texan accused of running the Silk Road's contraband bazaar, prosecutors called to the stand Michael Duch, a 40-year-old Silk Road heroin dealer from New York state. Duch told the court that he had been arrested in October of 2013, pleaded guilty to narcotics trafficking, and agreed to testify in the hopes of lessening his sentence. Duch, who went by the name Deezletime on Silk Road, had nothing to say about the defendant Ulbricht himself. Instead, he explained to the jury the dark details of selling highly addictive drugs on the website the government accuses Ulbricht of masterminding.

In just the six months from April to the end of September 2013, Duch sold more than 2,400 orders of heroin, totaling nearly 32,000 individual, 10-milligram "stamp" bags branded with names like "black magic," "murder," and "hot shots," he said. He made between $60,000 and $70,000 a month during that time, much of which went to his own serious heroin habit. And perhaps most importantly for the jury, Duch explained why the "safety and anonymity" of the Silk Road persuaded him to sell on the site despite having never sold drugs on the street.

"I saw the relative ease that came with it," he told the court. "It seemed like something I could get away with."

Duch also described how the Silk Road's customer base allowed him to reach buyers who he believed wouldn't have otherwise had access to his product. The prosecution showed an alphabetized list of hundreds of cities around the country that had received Duch's heroin shipments from a Monroe, New York post office, double-vacuum sealed and disguised with a fake return address. "Someone out in [a place like] Utah would be able to get heroin. The Silk Road made heroin available to them," Duch said.

Duch isn't the first Silk Road heroin dealer to tell his story. But telling it under oath in the cold light of a Manhattan courtroom, it could leave Ulbricht's jury with a grisly impression of the Silk Road's impact on its most deeply addicted users. At one point, prosecutor Serrin Turner read aloud from messages sent to Duch from his customers begging him to ship quickly as they slipped into withdrawal.

"I just want to check [on the shipment] because I am extremely dope sick and NEED something right now," read one message.

"I'm throwing up, the worst of the worst withdrawal symptoms, and plus I have life-destroying pain," Turner read from another.

Turner asked Duch if those sorts of messages were frequent. "I got these messages every day," he replied.

At the time, Duch had resorted to dealing to manage his own all-consuming drug habit, he told the jury. Starting as early as 2007, he had become addicted to painkillers prescribed by a doctor for sports injuries, and eventually moved on to snorting and then injecting heroin. By late 2012, he was buying painkillers from the Silk Road, which he says he heard about from news media. And as his own narcotics consumption escalated to a cost of $3,500 a week, he started dealing.

"I had an addiction," Duch said, with an expression of subdued pain he wore throughout his testimony. "I needed to feed it."

Duch says he would buy heroin in $6,000 "bricks" from a supplier he'd meet in Passaic, New Jersey, and then sell it online from his Silk Road account at a 100-percent markup. Though he also sold on dark web markets like Black Market Reloaded and Atlantis, he testified that 99-percent of his sales went through the Silk Road, because of its massive customer base.

Aside from offering a hands-on account of how the Silk Road worked from a dealer's perspective, Duch's story calls into question claims that the Silk Road reduced violence by moving drug sales from the street to the relative safety of the internet. Duch's testimony seemed to suggest that he wouldn't have sold drugs at all if it weren't for the Silk Road, and that–at least in his opinion—many of his customers wouldn't have bought them.

But it's also important to note that heroin may not have been a major seller on the Silk Road compared with less harmful drugs like marijuana and ecstasy. A study last year found that the most addictive drugs, such as heroin, methamphetamine and crack accounted for only a small part of the site's total revenue.

In its cross-examination of Duch, which had only started when court adjourned Wednesday evening, Ulbricht's defense attorney Joshua Dratel emphasized that Duch's testimony was the result of a deal with prosecutors. Without that deal, he argued that Duch could face 20 years in a mandatory minimum sentence for his high volume of drug sales and prior convictions.

Duch, who said he hasn't used drugs since his arrest in 2013, told the jury that his own health, his relationship with his girlfriend, and his career as an IT consultant all suffered from his heroin and painkiller use.

"The same drug that had impacted your life in this way, you were selling to thousands of people on Silk Road?" prosecutor Turner asked him.

"Yes, I was," Duch said. "It was something that bothered me on a daily basis."