Why is Henry Lee Lucas still considered a serial killer...?

When two Texas state attorney generals, former governor George W. Bush and more than 100 criminal investigators have stated, in some forum or another, that the guy was just mentally ill and confessing to crimes that didn't even exist, and then had nearly every murder that did exist in that area at the time tied to him, in which he confessed to - because he was mentally ill - just as he confessed to more than 500 murders that didn't exist. He was one of only one or two people that George W. Bush gave a stay of execution to, and he died of natural causes at the age of 64. But why is he *STILL* considered a serial killer when he never killed anybody and stands today as the danger of having police and prosecutors who do not understand or regard psychoses (For instance, Henry Lee not only confessed to more than 500 murders, he also claimed to be a "unicorn farmer" and "The king of Sweden", before being convicted of 12 or so murders that he confessed to, even though there was no evidence that he could had possibly been involved)