Klein defended his prosecutions by referring to a case where wheat giant Arthur Daniels Midland (ADM) acknowledged fixing prices.

"Technology changes, surely, and markets change, surely, but human nature doesn't really change. Businesses still have every incentive to collude and raise prices, and without the intervention of the government, they will do so," Klein said.

He played for the audience secretly taped meetings of top executives from ADM, the company that billed itself "The Supermarket to the World."

On the basis of those conversations, the Justice Department accused ADM of conspiring with other food producers to fix the price of lysine, an amino acid and an additive to animal feed. The tapes were released to the public last Friday, and showed the executives giggling as they discussed what the price of lysine should be in various markets.

In the tapes, the executives agreed to stagger their departures from the meeting so not to attract suspicion.

At one point, one of the executives joked an empty seat was being reserved for a FBI agent.

Listening to the tapes with the audience, Klein concluded the ADM case shows the need for strong governmental oversight of big business.

"What you were watching was by people who knew their behavior was illegal and posed substantial risks to the company. Can you imagine what they would do if it weren't illegal?" Klein said.