I want to know, what else does the government want to regulate the cryptocurrency blockchain for if the FBI can perform such a rigorous search on all the virtual accounts that have been created online by the couple? And found the private key linked to the wallet that received the funds, and they recovered over $3.5 billion and recorded it as the biggest seizure in the cryptocurrency niche.
I think the transaction the Government cannot track in the block-chain technology has not be made. FBI claim that they will endeavor to trace any fraudulent activity in the cryptocurreny network through their 21st century investigative technique. (I don't know what they mean by that)
Read:
https://www.justice.gov/opa/pr/two-arrested-alleged-conspiracy-launder-45-billion-stolen-cryptocurrency
The bitcoin community is thankful to the FBI that they helped those who lost their money because of this hack. It will increase the courage of people who want to adopt bitcoin for their personal lives and for their businesses.