Protesters gathered at a Manhattan court building on Tuesday in support of Ross Ulbricht, whose trial for being the accused mastermind behind what was once the internet’s biggest illegal drugs marketplace was beginning at a federal court inside.

Federal prosecutors accuse Ulbricht, who allegedly went by the alias “Dread Pirate Roberts”, of being the owner and manager of the deep-web marketplace Silk Road. He was arrested in a library in San Francisco in October 2013, and charged with drug trafficking, criminal enterprise, aiding and abetting distribution of drugs over the internet, computer hacking and money laundering.

According to the indictment, Ulbricht himself reaped “tens of millions of dollars” in commissions.

He is also charged with involvement in conspiracy to commission six “hits”, including against a former Silk Road employee, using bitcoin to pay the purported assassins. No killings were actually carried out.

In court, Ulbricht, clean-shaven and dressed smartly in a dark blazer and beige slacks, sat confidently beside his legal team. Occasionally he turned to flash a smile at his mother, Lyn, who was in the public gallery.

Ulbricht has consistently claimed that he was not Dread Pirate Roberts, and denies all the charges against him.

Outside the courtroom, protesters had gathered in support of Ulbricht.

Derrick J Freeman, who had come from Keene, New Hampshire, to demonstrate outside the court, told the Guardian he thought it would set a dangerous precedent if a website can be prosecuted for what its users do. “If so, drag Craigslist off to prison,” he said.

In its heyday, Silk Road was a sprawling marketplace where people used bitcoin to purchase a galaxy of different stimulants, hallucinogenics, opiates and prescription drugs.

In July 2013 it was estimated that transactions on Silk Road could be upwards of $30m-45m per year, and the indictment states that the site had “well over a hundred thousand buyers worldwide”.

It operated on the Tor network, a web anonymising service originally developed by the US naval research center and partly funded by Darpa as a way of protecting government communication.

For Freeman, if Ulbricht is actually Dread Pirate Roberts, he is a pioneer of the deep web, and a hero. “He brought the black market online,” he said. “There’s no fear of drive-by shootings, or back-alley stabbings.”