The charges against Saddam are mainly historical

According to, for example, New Zealand News - World - The charges against Saddam and BBC NEWS | Middle East | Charges facing Saddam Hussein, the charges to be filed by Iraq's new government against Saddam Hussein are mainly concerned with acts committed in 1991 or before. Only a vague charge of "Killing Political Activists over 30 Years" concerns more recent acts. Here are the actual charges.

• Invading Kuwait, 1990
• Suppressing Kurdish and Shi'ite uprisings, 1991;
• Anfal ethnic cleansing campaign against Kurds, 1987-88;
• Gassing Kurdish villagers in Halabja, 1988;
• Killing political activists over 30 years;
• Killing religious figures, 1974;
• Killing thousands of the Kurdish Barzani clan, 1983.

If one of our rationales for invading Iraq was to rid that country of a hated dictator, the charges don't reflect such a perception on the part of the new Iraqi government.