Prosecutors are asking a Manhattan judge to sentence a San Francisco man who created the online drug-peddling site Silk Road to decades in prison, while the defendant is asking to be freed soon enough to show he's a changed man.

Ross William Ulbricht, 31, is set to be sentenced Friday following his February conviction in federal court.

In a letter to U.S. District Judge Katherine Forrest, Ulbricht said he regrets what he calls a "very naive and costly idea."

He said he ruined his life and destroyed his future by what he now calls his "terrible mistake," and he promised to no longer be the "rebellious risk taker" he was if he is given less than the life sentence recommended by the Probation Department.

"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," he wrote.

Prosecutors, though, asked for a sentence substantially longer than the 20-year mandatory minimum, saying Ulbricht "developed a blueprint for a new way to use the Internet to undermine the law and facilitate criminal transactions" before he was nabbed in a San Francisco library in 2013, two years after launching Silk Road.

He was convicted of seven drug and conspiracy counts by a jury that deliberated only three hours.

Prosecutors said Ulbricht collected over $18 million in bitcoin commissions operating a website with thousands of listings under categories like "Cannabis," ''Psychedelics" and "Stimulants." They said he brokered more than 1 million drug deals worth $213 million.

To support a lengthy sentence, prosecutors said in a legal brief that Ulbricht's massive narcotics-trafficking enterprise had resulted in at least six drug-related deaths, including a 27-year-old Microsoft employee and a 16-year-old boy in Perth, Australia. They also said he solicited multiple murders for hire in attempts to eliminate perceived threats, though authorities found no evidence anyone was killed.

"The site enabled thousands of drug dealers to expand their markets from the sidewalk to cyberspace, and thereby reach countless customers whom they never could have found on the street. The consequence was to vastly expand access to illegal drugs," prosecutors said.