I'm not sure if I understand how one follows from the other.
What I am suggesting is that if President Bush was 100% convinced that Saddam Hussein had weapons of mass destruction, he would much rather Saddam was jailed rather than executed so that he could have him questioned about the locations of the WMD's that they have so far failed to find. The fact that President Bush (or the White House rather) made a statement welcoming the sentence makes me think that President Bush is admitting there are no WMD's