After Ross' arrest they found the file LEcounterintel.doc on his pc, where he wrote about getting insider information from a cop.

Link:
https://www.google.com/search?q=Carl+Mark+Force&ie=utf-8&oe=utf-8
http://www.justice.gov/sites/default/files/opa/press-releases/attachments/2015/03/30/criminal_complaint_force.pdf
http://www.wired.com/2015/03/dea-agent-charged-acting-paid-mole-silk-road/

Edit: Along with the criminal complaint there were released some more chat files with VJ. Dunno the links atm.