I think they were found competent to stand trial. Wouldn’t that preclude insanity?
No, for three reasons:
(1) It is the judge who decides competency to stand trial, and the jury which decides an insanity defense.
(2) Competency to stand trial is judged as of now, and insanity is judged as of the time of the crime.
(3) The law asks different questions for each issue: to be competent to stand trial, you have to understand that you are on trial for a crime and be able to communicate with your lawyer; to be sane enough to be found guilty, you have to have known what you were doing and have known that what you were doing is wrong. It is therefore possible for someone to be incompetent to stand trial and yet be legally "sane," and vice versa.
Both of those issues are very hard for a defendant to prove; many people who are absolutely batspit crazy are both legally sane and competent to stand trial. Jeffrey Dahmer, for example, was found both competent to stand trial and legally sane, but you are not going to convince me that he was psychologically normal.
No. That just means they are sane now to understand the trial and charges.