Ask HN: Are Bitcoins untraceable to a real identity?

I am not sure I understand bitcoins correctly.

Say ransom-ware attacker asks for 10 bitcoins to be sent to address 123. Then the attacker wants to convert the bitcoins to dollars. On the bitcoin exchange he buys x dollars and transfers the dollars to a bank account. Doesn't the exchange know that such dollars where paid with bitcoins from 123 address and also knows the identity of the bank account owner? Even if the attacker moves bitcoins between addresses before exchanging them, doesn't the block-chain save the history of transfers of bitcoins from and to all addresses? So, if I know the original bitcoin address and a path that leads to a bank account, I know the identity of the attacker (or someone related to the attacker)?