Organised internet crime gangs trojan your laptop and get access to your online banking. They buy hundreds of coins from themselves with YOUR money. When you discover and tell your bank, can the bank look and see where the money went?No. The bank will probably be able to see which vendor or market was used to buy BitCoins but from then on that vendor will only see to which random address BitCoins were sent to which there's no name, address or IP address attached.
Columbian drug gangs deposit huge bags of hundred dollar bills in a St Maarten bank account. That bank has a USD account on Wall St. They convert the dollar bills to credit in their Chase Manhattan account and buy hundreds of coins from their Barclays account in the UK. American officials then raid the St Maarten bank. Are they able to notify Barclays?If in your example Barclays is selling BitCoins and if the Columbian drug gans have already received their BitCoins it's too late. Nothing that you or Barclays can do about it anymore to get the BitCoins back.
An arms company in Germany wants to take a contract from the Iranian Revolutionary Guards to supply 5000 machine rifles. They know that while this kind of arms sales are legitimate business in Germany, it is illegal to trade with the Iranian regime. Can they use bitcoin to collect on the contract?Yep and it's perfectly "legal". If they have BitCoins that they received from the Iranians and can find buyers and sell them for EUR they can cash in and no one will ever be able to make a connection to where those BitCoins came from. In fact there already is a service which sole purpose is to receive BitCoins from various addresses and then randomly send them out in correct amounts to the targets of their clients so that in your example if Iranians used it their BitCoins might have ended up with Joe sixpack and the Germans received BitCoins from me. Beautiful isn't it?