In an interview, Andrew Lo says,

There is one very simple question that you can ask — which has a definitive answer — about the small number of individuals who were responsible for managing this group at JP Morgan and putting on the specific trades that lost these large amounts of money. That question is: How were they compensated on an annual basis? Were they paid a salary and a bonus, and was the bonus a function of the profitability of the group, or was the bonus a function of the hedging ability of the group? If you can answer this question — and it definitely has an answer to it; it’s not a metaphysical question — you will have your answer as to whether it was proprietary trading or hedging. I don’t know the answer, but I know the answer exists, and I know that certainly the government can get that answer with a single phone call.

My claim is that with principles-based regulation, you could be asking this question ahead of time during an onsite audit.

Pointer from Mark Thoma.