How to make cryptocurrency easier for law enforcement?
It is possible to mitigate criminal elements in existing cryptocurrency networks within the current regulation framework. 


Addresses of results of criminal actions are well known. Think stolen Bitstamp funds. Eventually these are written to police reports somewhere.
Exchanges, and other respected corporations, should act as a gatekeepers in this community off their own interest. Authorities of financial institutions have a duty to report crime (Misprision of felony).
If any exchange process transaction that has gone through a blacklisted address, the transaction should be stopped and the actor should go through anti-money laundering process, because they have somehow got criminal assets in their hands. There should be a paper trail to follow. If exchanges do not do this then they should be themselves subject to money laundering investigation due to breaking local AML and KYC regulation.
Tracking back Bitcoin transactions to blacklisted addresses is technically very feasible, because all transactions are public and it is just matter of maintaining a tree of transactions in computer memory. It doesn't matter how many times you tumble your coins, because you simply can't eliminate the trace of transactions from blockchain.
This assumes there is a party (Interpol, FBI) who maintains and enforces a known black list of addresses. The list should be publicly available for anybody. The list contains addresses compiled from police reports world wide. Currently no no such party exist. All parties in global trusted police consortium should be able to add addresses on this list with reference back to a local police report.
Fungibility, as promoted by some Bitcoin advocates, does not exist. You simply can't say "I don't know where my money is coming from." to government officials. Banks and financial institutions like PayPal are already subject to this regulation.


This way the system would be opaque to every day transactions (think a transaction of hiring divorce lawyer, medical bills) but still having a mechanism to track down criminals.