There was no moral justification in attacking Iraq. We were not attacked by Iraq's military, nor were ANY of the 9/11 terrorists citizens of Iraq. None of our allies were attacked by Iraq. No Iraqi military units were in a position to be a direct and immediate threat to US or our allies. The Administration knew, had reason to know, or should have known, because they were informed by UN weapons inspectors that iraq was not in possession of WMD, was not expanding its nuclear program, etc., which later US forces inspections proved.
The Administration engaged in fraud through the use of perjured testimony and deliberately false information to obtain UN sanction for the invasion. By US law, any fraudulent activity is a crime. Using fraud to obtain an appearance of legitimacy is a crime which usually translates to illegal.