To explain better my question, consider this example:
- Individual A is an investigator
- Individual B is been investigated
Faking to be interested B's service, individual A gets B's public key to pay for his service.
As the system is opened for everyone to see the transactions, it is possible to track all the transactions that happened using that public key, and mainly it is possible to track all the transactions with that public key from now on.
In this case, the only way to be anonymous would be create a new pair of keys for every transaction, and never centralize the bitcoins, is it right?