slander

Lawrence Neil Rogak

It's hard to answer your questions without more details, but generally speaking, the credibility of an expert witness is something that the jury decides -- or, if there is no jury, then the judge. I wonder if you actually mean the qualifications of the expert, instead of his credibility. If that's what you're talking about, a witness gets qualified as an expert by testifying, in court, as to his or her background and experience. The judge then decides whether the witness is sufficiently qualified as to the issues in the case, to be allowed to testify as an expert witness. Whatever claims an attorney may make about the qualifications of an expert, it is ultimately the judge who decides if the expert is qualified.

Benjamin Kirke Sanchez

I generally agree with Lawrence's answer, but would like to add to it. The very role of an attorney is to advocate for his client, which includes discrediting the opposing expert if at all possible. There's a lot of material that can be used to discredit an expert, including some that you may think otherwise objectionable. If an expert lies about personal issues not related to the case at hand, it still may bear on the expert's credibility. Without more information, it's hard to give you a more specific answer other than to say that lawyers have a lot of leeway to try to discredit an alleged expert.

Sharon Elizabeth Chirichillo

Concur with other answers. An attorney making unsubstantiated claims about the credibilty of a scientist/expert withness involved in a DUI case will go to weight. That means the jury will decide whether the attorney's claims have any merit. Advocacy is a fine art. If an attorney is questioning the credentials of a witness that certainly is acceptable and expected.

Paul D Friedman

It depends on the statement and the jurisdiction. If the statements occur during a court hearing or pleading, the attorney may be immune or subject to qualified immunity. In most jurisdictions, statements made in a hearing are not subject to defamation actions. However, some jurisdiction follow Federal Rule 11 in which the attorney must make a reasonable investigation before making a statement or be subject to disciplinary or court action for making a frivolous claim or statement.

Scott Kenneth Petersen

It's fair game for a lawyer to ask questions about the background and experience of any expert witness, sources relied upon for that expert's opinion, familiarity with the facts of the case, prior cases in which that expert has testified and rendered an opinion, as well as that expert's bias, interest or motive (i.e. how much that expert is being paid for his testimony). It is difficult to tell what you mean be "unsubstantiated" claims regarding credibility, but it is improper for example for a lawyer to express any personal opinion regarding any witnesses credibility or to impune to the credibility of an expert on bases not revealed by the evidence (i.e. a claim in closing argument that "all expert witnesses are hired guns, etc"). The attorney who calls the expert to testify should make timely and proper objections to improper attacks on any witnesses credibility.