Six people who died from overdoses bought drugs via the online Silk Road marketplace, claims the US government.
Sited on the dark web, the Silk Road was a marketplace for illegal drugs that was closed in 2013, after the FBI arrested its creator - Ross Ulbricht.
The claim was made in court papers filed by the US government prior to the sentencing hearing for Mr Ulbricht.
Mr Ulbricht was convicted of narcotics and money laundering charges in February 2015.
The maximum sentence he faces for these crimes is life in jail.
In its testimony at the 15 May hearing, the US is also planning to let parents of two of the deceased testify.
Defence lawyers acting for Mr Ulbricht are seeking to delay the sentencing hearing while they evaluate the evidence the US government has amassed to make its claims about overdose deaths.
Lawyer Joshua Dratel, who is representing Mr Ulbricht, said the information provided by the US government was "woefully incomplete". Mr Dratel is asking for a delay of a month while he gathers expert witnesses and other testimony to counter the claims.
In defence court papers quoted by tech news site Ars Technica, Mr Dratel said it planned to argue that the Silk Road had in place policies that tried to limit the risk faced by those buying drugs.
The Silk Road was in operation from 2011 to 2013 and was available via the Tor dark web network. Payments for drugs and other services on the site were made with bitcoins. Mr Ulbricht is believed to have made about $18m (£12m) from running the site.