Hmm haven't we discussed this to death?
It is not possible for the police or any entity to tell, just by looking the transactions themselves. In fact, without any actual link to evidence, the transactions can't be identified. If the authority can get one of the addresses/transactions involved, they could get the whole link of addresses that are related but that isn't possible all the time and its rather inaccurate and useless.
This is why bitcoin cannot be legalized in some countries since there are people who use bitcoins in form of illegal transactions, it cannot be tracked by the government. It is considered as a haven for black markets and money laundering by the government.