A study comes out that implicates benzene with cancer. Several oil companies pool 27 million dollars to fund their own research into the matter.
Here's where it gets ugly. The oil companies hire a guy to lead the research who expects to find a result favorable for the oil companies. Further, his ongoing funding is contingent on pleasing the oil companies. And the clincher... if the oil companies don't like the results, they can bury the data.
Let me summarize that: collect an obscene amount of money, pay a guy only if he produces data you like, and hide the data if it looks bad. And you wondered why it took 50 years to prove smoking is bad for you.
http://www.chron.com/cs/CDA/ssistory.mpl/front/3159505