Even though it did not appear a WMD program might be in place, what did Hussein do that increased the fears of weapons inspectors?

He didn't allow inspectors to check his facilities and institutions which inspired fear that he was producing weapons of mass destructions and biochemical weaponry even more. In the end, it turned out however that he did not have them and that the technology he owned was way way behind what was initially expected. He just hid it so he could inspire fear so people wouldn't bother him.