https://btcmanager.com/bitcoin-transactions-analysis-breaks-tor-anonymity/
Relevant parts:
"It is quite ironic how Bitcoin had been stigmatized in the past as an anonymous payment method that enables criminal activity and money laundering. In fact, we now understand that the opposite is true. Bitcoin is practically a gift for law enforcement agencies with access to big data. Not only can bitcoin transactions be analyzed to expose criminal activity currently taking place over Tor, but transactions made in the past can also be analyzed to reveal, in accurate detail, who did what, and when, from where. If no statute of limitations is in place for the specific illegal activity, then bitcoin can be a tool that law enforcement agencies can use to track down every prosecutable felony and misdemeanor accomplished with bitcoin over Tor since the creation of the network."
Bullshit.