Bitcoin works with an unprecedented level of transparency that most people aren't used to dealing with. All Bitcoin transactions are public, trackable and are permanently stored on the Bitcoin network. Bitcoin addresses are the only information used to define where bitcoins are allocated and where they are sent. Each user's wallets create these addresses privately.
However, once addresses are used, they become tainted by the history of all the transactions in which they participate. Anyone can view the balance and all transactions from any address. Since users often have to reveal their identity to receive services or goods, Bitcoin addresses cannot remain completely anonymous. Since blockchain is permanent, it's important to note that something that can't currently be tracked may become trivial to track in the future.
For these reasons, Bitcoin addresses should only be used once and users should be careful not to reveal their addresses. The men were caught converting their bitcoins into euros in bank accounts using Bitcoin trading services and then withdrawing millions in cash from ATMs. In this case, it's a Bitcoin mixer, which ensures that it's more difficult to make Bitcoin trackable. Through blockchain explorers, Bitcoin transactions can be easily tracked, but it's becoming increasingly difficult to conduct Bitcoin transactions anonymously.
