Prosecutors for the trial against Silk Road creator Ross Ulbricht have asked the judge for a sentence "substantially" longer than the 20-year minimum to "send a clear message" to anyone who wants to follow in his footsteps and build their own drug-dealing dark web empire.

Just three days before Ulbricht is expected to be sentenced to between 20 years and life in prison, the 16-page letter to Judge Katherine Forrest highlighted that, this being the first trial of its kind, the court has the opportunity to set an example and send out a message that will dissuade others who think they can hide illegal websites from the police.

"Ulbricht's conviction is the first of its kind and his sentencing is being closely watched. The court thus has an opportunity to send a clear message to anyone tempted to follow his example that the operation of these illegal enterprises comes with severe consequences," the letter reads.

It asks for Judge Forrest to impose a sentence "substantially above the 20-year mandatory minimum, in order to reflect the seriousness of the offence, to promote respect for the law, and to afford adequate deterrence to criminal conduct."

'Please leave me a light at the end of the tunnel'

The letter comes just a day after Ulbricht himself pleaded with Judge Forrest to not hand down a sentence of more than 20 years. The 31-year-old, who has been in police custody since October 2013, said he understood the "the terrible mistake" he had made in creating Silk Road as an anonymous website where almost anything could be bought and sold. Ulbricht accepted that the judge "must take away my middle years," but pleaded for her to "leave me my old age."

Ulbricht went on: "Please leave a small light at the end of the tunnel, an excuse to stay healthy, an excuse to dream of better days ahead, and a chance to redeem myself in the free world before I meet my maker."

His plea accompanied a flood of sympathy sent to Judge Forrest, who has received over 100 letters from Ulbricht's friends, family and fellow inmates praising his good nature. But countering these – and claims that Silk Road's eBay-style user feedback system made it a far safer place to deal drugs than in person on the streets – the prosecutors once again point to Ulbricht's alleged solicitation of multiple murders-for-hire, charges not included in the sentencing this week. "He was willing to use violence to protect his enterprise... At no point has he acknowledged full responsibility or shown true remorse for his actions."

Akin to a heroin dealer handing out clean needles

They say Silk Road's rating system "provided a veneer of safety to an intrinsically unsafe business. Even if rated 'five out of five,' heroin is still heroin... Indeed, praising Silk Road for including 'harm reduction measures' is akin to applauding a heroin dealer for handing out a clean needle with every dime bag."

Prosecutors also claim Silk Road was directly responsible for six deaths caused by overdosing on drugs bought from the site, although Ulbricht's lawyer, Joshua Dratel, counters these claims by saying the evidence contained "gaping holes" and even pointed to Fernando Caudevilla, a doctor who regularly posted advice about taking drugs on the Silk Road forums as examples of Ulbricht not wishing to cause harm.

For the first time in Ulbricht's trial, the prosecution pointed to how Silk Road's closure spawned the opening of Silk Road 2 (which was also shut down by the FBI) and numerous other drug-dealing websites on the dark web, accusing Ulbricht of creating the blueprint for them. They wrote: "Using that blueprint, others have followed in Ulbricht's footsteps, establishing new 'dark markets' in the mould of Silk Road, some selling an even broader range of illicit goods and services than Silk Road itself."

Ulbricht will be sentenced in New York on 29 May at approximately 13:00 (18:00 UK time).