Changes rules for expert testimony in criminal cases

(1)Existing law allows a person who is unlawfully imprisoned or restrained of their liberty to prosecute a writ of habeas corpus to inquire into the cause of their imprisonment or restraint. Existing law allows a writ of habeas corpus to be prosecuted on the basis of false evidence that is substantially material or probative to the issue of guilt or punishment that was introduced at trial. Existing law defines false evidence for these purposes as including the opinions of experts that have been repudiated by the expert or that have been undermined by later scientific research or technological advances.

This bill would expand the definition of false evidence to include the opinions of experts that are undermined by scientific research that existed at the time of the expert’s testimony and opinions for which a reasonable dispute has emerged within the expert’s relevant scientific community as to the validity of the methods or theories upon which the expert based their opinion.

(2)   Existing law limits the testimony of a witness who is testifying as an expert to matter that is of a type that reasonably may be relied upon by an expert in forming an opinion upon the subject to which the expert’s testimony relates. Existing law allows a witness testifying in the form of an opinion to state on direct examination the reasons for their opinion and the matter upon which it is based.

This bill would require a court in any criminal proceeding, when considering whether expert testimony is based on matter that is of a type that reasonably may be relied upon by an expert in forming an opinion, to determine whether the expert’s opinion and any supporting literature, studies, research, or other bases on which the expert relies in forming their opinion are based on a reliable foundation, properly tested methodology, and sound logic, as specified. The bill would specify that an opinion or any supporting literature, studies, research, or other bases that lack a reliable foundation, properly tested methodology, and sound logic are not matter that may reasonably be relied upon. The bill would specify that if a portion of the expert’s testimony extends beyond the underlying support, the court may allow the portions of the testimony that do not extend beyond the underlying support if they are otherwise admissible.