The lions share was in hedging just after the Amaranth Advisors implosion. Lot of production got locked up at low cost. Not much left on the spot market so speculators did rule as they could easily drive prices in a low float environment.
We were due for a correction on prices. It was probably a lot of things. Reduction in subsidies by China, regulation number of cars in Beijing. Demand fall off in the US, but the big one was probably the nonrenewal of hedges or a cash in of the chips on them. It gets more expensive to hedge the higher prices go and eventually you have to stop. Add in a well timed public outcry of speculation. Traders probably saw too many open contracts and realized what was happening.
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