https://www.lexology.com/library/detail.aspx?g=019e4e0f-fddb-4097-895c-c872bbbdcb3aJurisdiction
Although BTC-e is not a US company, FinCEN asserted jurisdiction because BTC-e conducts business as an MSB in substantial part within the United States. More specifically, FinCEN regulates as money transmitters (MTs) any person in the business of accepting currency, funds, or any substitute for currency from one person and transmitting such currency, funds, or substitute for currency to another person or location (unless an applicable exemption applies). To establish jurisdiction, FinCEN asserted that:
Since 2011, BTC-e customers located within the United States conducted at least 21,000 virtual currency transactions worth over $296,000,000.
These transactions included funds sent from customers located within the United States to recipients who were also located within the United States.
These transactions were processed through servers located in the United States.
BTC-e attempted to conceal that it provided services to customers located within the United States.
BTC-e instructed customers to make use of correspondent accounts held by foreign financial institutions or services provided by affiliates of BTC-e located abroad.
The whole thing is BS, the fiat went to overseas companies, eg OKPAY in the UK, and then to BTC-e. The crypto, which isn't legally money under the US constitution, is a virtual construct with no fixed address.