Question: I was recently party to a preliminary hearing in a criminal case in which a 911 call was played. The content of the 911 call was very beneficial to the defendant. During the hearing, the judge said something to the effect of, "It would be a question for the jury whether the caller was 'being honest.'"

In other words, the judge was suggesting that the caller to the 911 was being disengenuous and deliberately conveying a false impression -- something that I think would never occur to most people because the call seemed completely genuine. Also, the caller would have had no motive to faking their mental state. I got the idea that the judge was looking for some angle to discredit the 911 call out of interest to see the defendant convicted.

In any case, from the judge's remark I got the idea that he might say something like that during the trial, or give the jury an instruction designed to make them think the 911 caller was putting on an elaborate act.

Is a judge allowed to do this?

Answer: 
It is the jury's job to evaluate the credibility of the witnesses, and it is the judge's job to inform them of that responsbility.

It is not appropriate, however, for the judge to indicate to the jury what answer they should come to on those questions.

In [*Quercia v. United States*, 289 U.S. 466 (1933)](https://supreme.justia.com/cases/federal/us/289/466/), the defendant in a drug case took the stand to deny the charges. Before the jury went to deliberate, the judge made the following observation:

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> I am going to tell you what I think of the defendant's testimony. You may have noticed, Mr. Foreman and gentlemen, that he wiped his hands during his testimony. It is rather a curious thing, but that is almost always an indication of lying. Why it should be so we don't know, but that is the fact. I think that every single word that man said, except when he agreed with the Government's testimony, was a lie.
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The jury convicted, but the U.S. Supreme Court reversed, holding that the instruction was an error. It said that the judge has the right, generally speaking, to comment on the evidence, but that right is not unlimited, because juries are likely to be swayed by the judge's assessments, even if he instructs them to make their own decisions:

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> The influence of the trial judge on the jury is necessarily and properly of great weight and his lightest word or intimation is received with deference, and may prove controlling. This court has accordingly emphasized the duty of the trial judge to use great care that an expression of opinion upon the evidence should be so given as not to mislead, and especially that it should not be one-sided; that deductions and theories not warranted by the evidence should be studiously avoided.
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The comment you seem to be imagining is a closer call than this, but I think most judges would agree it would be inappropriate.

At a preliminary hearing, though, where there is no jury, there is no real problem with the judge making that comment. If I were the defense attorney, I'd be glad he did, as it would help inform my decision about whether to pursue a jury trial or a bench trial.
There is a concept of [implicature](https://en.wikipedia.org/wiki/Implicature) that says that meaning is conveyed not only by the meanings of the words, but by the circumstances that are likely to cause someone to utter those words. There is nothing in the literal meanings of the words that says that the witness is lying. Your belief that it conveys that seems to be based on implicature: the judge would not feel compelled to mention it unless they thought the witness is lying.

However, that is not necessarily the case. Certainly if for one witness and one witness only, the judge were to say this without anything else giving them reason to, it could come across as implying that the witness is untrustworthy. On the other hand, if the judge were to say this each time a witness takes the stand, or say it at the very beginning of the trial and indicate that it applies to all witnesses, or say it when prompted by something more than just the witness testifying, such as a party asking the judge to make a decision that they believe relies on an assertion of fact, then this inference is less valid.