The basis is generally that fact witnesses are precluded from assuming the role of the jury. It is up to the jury to decide, for itself, whether or not it finds Zimmerman's account to be credible.
The "witness vs. defendant" distinction doesn't save that encroachment on the jury's turf. Probably makes it worse.
Would you feel the same way if Serino said he thought Zimmerman was a pathological liar?
I would want to know why he thought that, because there is no evidence of that. There was no basis on him even using that phrase at all, as MOM demonstrated directly after.
But yes, I think that asking a police detective if he thought the person he was investigating was being truthful or lying is a legit question. If he thought Zim was a pathological liar, then provide the basis for the formation of that opinion in detail.
I do not understand why this testimony was stricken, but the testimony of a proven perjurer, Rachael, was not, nor has she been charged with perjury or manufacturing evidence or conspiring to manufacture evidence in the form of that letter.
Okay, the witness cannot testify to his opinion of the defendant's truthfulness. But then why is it okay for the prosecution to ask if the comments made by the defendant showed "spite or ill will" toward the victim? Isn't that also asking for an opinion of the state of mind of the accused? How is the witness qualified to testify to one but not the other?
But the same witness was allowed to claim that Zimmerman was motivated by ill will.
Part of a cop's job is to be able to pick up on non-verbal cues which indicate when a witness is being truthful. Although some cops may claim to perceive such clues because they want to justify a belief a defendant is lying, the presence or absence of such cues would be a bona fide subject of direct observation by the cops.
I guess I would regard a question of "Did you perceive Zimmerman to be truthful" as a short-hand form of "What non-verbal cues, if any, did you notice from Zimmerman which would influence your judgments of his truthfulness"? If a cop were to say a witness was a pathological liar, a proper cross-examination would ask what non-verbal cues led to that opinion. If the cop can't articulate any clear basis for such belief, the defendant should be allowed to argue that the jury should consider it plausible that the cop might have formed an erroneous opinion of the defendant which was not based upon any real evidence, and the imagined the defendant as acting in such fashion as to justify that opinion.
If the prosecution asked that question of a prosecution witness, maybe you might have a case. . . .calls for a conclusion by the witness. OTOH if Im not mistaken, the question was asked by the defense, of a nominally hostile witness for the prosecution. Im at a loss to know why it is reversible error if the prosecution doesnt make a timely objection?
And, BTW, the defense established (or at least I thought it had) that the investigation was headed nowhere until Crump announced that he had "found a witness in the lovely and gracious - and articulate - "Dee Dee. Is the jury not entitled to the information that the prosecutions whole case hinges on the credibility of Dee Dee"?