Notice this exchange from Sheriff Dupnik’s interview by Katie Couric (the one K-Lo cited earlier):

Couric: But some people would say you are overly-politicizing this situation. That it appears at this juncture, although it’s unclear, that this was a lone, deranged individual that might not have been inspired to do this at all for political reasons.

Dupnik: We’ll never know the answer to that because there’s no way to get into the heart and soul of a person to find out what their true motive is. And second of all, we’re dealing with a very troubled personality.

One needn’t be an experienced law-enforcement type to know two obvious things at this point:

(1) It is common for the state to prove motive in a criminal case, particularly a homicide case that requires proof beyond a reasonable doubt of specific intent to kill. Evidence of motive is not required, but prosecutors almost always try to prove it because juries want to be confident, before convicting someone of a serious crime, that they know why the defendant acted. And

(2) Loughner’s counsel will almost certainly go with an insanity defense, since there seems to be no other possible defense. That is, the case will be all about the operation of his mind: motive, intent, and capacity.

Insanity defenses try to suggest to juries that the defendant was so delusional he could not form cogent thoughts. Motive evidence can be powerful rebuttal. If there was a logic to why Loughner chose Rep. Giffords as a target — e.g., political positions she took that offended him — it could be critical to the prosecution’s ability to prove that he acted with criminal intent, to prove that his acts, while horrific, were purposeful. A juror doesn’t have to agree with a murderer’s motive in order to conclude that the murderer did have a motive that was tied to reality and was acting out of evil intent rather than out of a disconnection from reason. This could be the difference between conviction and a verdict of not guilty by reason of insanity.

While I’m sure we’re all very impressed with Sheriff Dupnik’s thoughtful views on gun policy and right-wingers, his day job is law enforcement. A large element of that job is to maximize the chances that the guilty will be convicted (to say nothing of the duty to avoid prejudicing the jury pool). How does it help matters for him to be telling the media that, in his vast experience as an investigator, he has learned that we can never really know what motivates people to act? That motive evidence is sheer speculation? That in his opinion, Loughner is “a very troubled personality” — a statement that will surely be used by the defense to argue that even those running the investigation concluded that the defendant was insane?

If Loughner was non compos mentis, it will be his counsel’s job to establish that, and she will be given every opportunity to do so under criminal due process rules — rules that are especially generous in capital cases. Sheriff’s Dupnik’s role at this point is to keep his mouth shut and collect evidence, not run off at the mouth for the benefit of the defense. We shouldn’t be hearing anything from him unless and until charges are filed, and even then his comments should be limited to what is in the public record. If he wants to be a pundit, he ought to resign from law enforcement and go be a pundit.