Of course he had WMDs. We, along with other countries, gave him sarin gas, etc. That doesn't excuse George W Bush's excuse to invade in 2003. At that time, the argument was that Saddam was trying to get nuclear weapons, they were an "immediate threat" to us, and were somehow conected to 9/11. All turned out to be false.
For Al-Janabi's testimony, it's not even a matter that the administration didn't fact-check enough, they were looking for ANY excuse to invade Iraq. In fact, I read on CNN that we already had plans on the table before 9/11 even happened(according to cabinet member Paul O'Neill).