Gwynne Dyer, is noted Military historian and a commentator on international affairs. In a recent article in a Vancouver paper, he proposes that Saddam was tried and executed for the Dujail murders, because the west and the US was implicated in the other crimes he committed.

From The GeorgiaStraight:
"It was not the Iraqi government but its American masters that chose to execute Saddam Hussein in a great rush as soon as the first sentence was confirmed, thus cancelling all the other trials on far graver charges that awaited him. The current Iraqi government had nothing to hide if those trials went ahead; the United States government did.
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With all of Saddam’s other crimes to choose from, why on earth would you hang him for executing the people suspected of involvement in the Dujail plot?

Because the United States was not involved in that one. It was involved in the massacre of the Iraqi Communists. (The U.S. Central Intelligence Agency gave Saddam their membership lists.) It was implicated up to its ears in Saddam’s war against Iran—to the point of arranging for Iraq to be supplied with the chemicals to make poison gas, providing Baghdad with satellite and AWACS intelligence data on Iranian targets, and seconding U.S. air force photo interpreters to Baghdad to draw Saddam the detailed maps of Iranian trenches that let him drench them in poison gas.

The Ronald Reagan administration stopped Congress from condemning Saddam’s use of poison gas, and the U.S. State Department tried to protect Saddam when he gassed his own Kurdish citizens in Halabja in 1988, spreading stories (which it knew to be false) that Iranian planes had dropped the gas. It was the U.S. that finally saved Saddam’s regime by providing naval escorts for tankers carrying oil from Arab Gulf states while Iraqi planes were left free to attack tankers coming from Iranian ports. Even when one of Saddam’s planes mistakenly attacked an American destroyer in 1987, killing 37 crew members, Washington forgave him.

And it was George W. Bush’s father who urged Iraq’s Shias and Kurds to rebel—after Saddam was driven out of Kuwait in 1991—and then failed to use U.S. air power to protect the Shias from massacre when they answered his call. The U.S. was deeply involved in all of Saddam’s major crimes, one way or another, so no trial that delved into the details of those crimes could be allowed."
http://www.straight.com/article/saddam-hussein-hanged-for-the-wrong-reason