UK Attorney General advice on Iraq

Why is not Iraq's hard factual evidence of non-cooperation and actual obstruction rather than hard physical evidence of arms sufficient to legally justify war?

After all, the ceasefire they signed in the first Iraqui war and many UN resolutions talk about complete cooperation being required. Not only did we not see cooperation but we saw actual obstruction from Iraq.

We had plenty of hard and clear evidence of Iraqui non-compliance!