It's all chronicled in Ross's DMs:
"The hitman scam: Dread Pirate Roberts’ bizarre murder-for-hire attempts" https://arstechnica.com/tech-policy/2015/02/the-hitman-scam-...
It's worth pointing out the hitman allegations weren't part of his trail which ended up with a two life terms + 40 years sentence (the hitman charges were dropped, presumably because it was pointless as he was already in prison for life). Considering that, it does seem an excessively harsh punishment.
[1]: https://freeross.org/misinformation/
Relevant part cited:
The accusations relied on anonymous chats and text files never proven to have been authored by Ross. Hard evidence and testimony—including from the lead Silk Road investigator—show that, over time, multiple people were behind the site admin’s handle (who was called Dread Pirate Roberts or “DPR” for short). Two corrupt investigators (sent to prison) also had unfettered access to Silk Road and were admittedly involved in numerous plots.
Ross has always denied being involved with these allegations, and even Curtis Green, the only alleged victim ever identified, is a longtime, fervent supporter of Ross’s release.