Here is the relevant section from the Times article on the IRS agent that figured it out:
Mr. Alford’s preferred tool was Google. He used the advanced search option to look for material posted within specific date ranges. That brought him, during the last weekend of May 2013, to a chat room posting made just before Silk Road had gone online, in early 2011, by someone with the screen name “altoid.”
“Has anyone seen Silk Road yet?” altoid asked. “It’s kind of like an anonymous Amazon.com.”
The early date of the posting suggested that altoid might have inside knowledge about Silk Road.
During the first weekend of June 2013, Mr. Alford went through everything altoid had written, the online equivalent of sifting through trash cans near the scene of a crime. Mr. Alford eventually turned up a message that altoid had apparently deleted — but that had been preserved in the response of another user.
In that post, altoid asked for some programming help and gave his email address: email@example.com.