This is one of our editors' picks from our ongoing roundup of Investigations Elsewhere.

In 2002, the Supreme Court ruled that the execution of mentally disabled convicts was unconstitutional, spurring a string of appeals by death row inmates. In Texas, a psychologist named George Denkowski testified in nearly two-thirds of those appeals. But Denkowski, who was known as state prosecutors' go-to psychologist, now stands accused of using "junk science" -- and some of the men he assessed have already been executed, reports the Texas Observer.

The success rate for appeals based on the Supreme Court’s ruling is 40 percent nationwide; in Texas, it is just 28 percent. Of the 29 men he evaluated, Denkowski concluded that eight were mentally disabled – about 28 percent.

In an interview between the psychologist and Daniel Plata, an inmate then on death row, the Observer reports that Denkowski repeatedly made "assumptions during the testing that would inflate Plata's scores." The cutoff for mental disability is an IQ of 70, which is what the test determined Plata had. But Denkowski then bumped that figure up to 77, based on other considerations. For instance, the test measures a subject's ability to do things like count money or groom himself. Denkowski said that Plata "was just never taught and required to do a lot of these things. So I don't think that's a genuine deficit."

Denkowski did not respond to the Observer's requests for an interview, but he has argued, as the Observer puts it, "that the test manuals produce skewed results because they offer no guidance on how to take such psychological and cultural factors into consideration."

The federal judge in Plata's case determined that all of Denkowski's testimony "must be disregarded due to fatal errors." Afterward, one of the psychologist's colleagues filed a complaint against him with the Texas State Board of Examiners of Psychologists.

If Denkowski loses his license, 17 men on death row may have their cases re-evaluated, according to the Observer. But some have already been executed. In one case, Denkowski first determined that an inmate was mentally disabled but changed his mind when prison guards found books in his cell. The inmate said later that he stacked the books to use as a chair.