Why did Judge Tate use three Garden City doctors to pronounce a verdict upon the mental capacities of the prisoners?

According to the text, Tate followed protocol and did what the law required. He wasn't willing to go outside the box or request outside assistance. We can also infer that he hadn't been won over by the field of psychiatry.... to Tate, a doctor was a doctor (my opinion).

”Judge Tate did not entirely deny the motion; rather, he did exactly all the law demanded by appointing a commission of three Garden City doctors and directing them to pronounce a verdict upon the mental capacities of the prisoners."