Trial testimony: expert witnesses: writ of habeas corpus.

(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 specify that an expert opinion based on circular reasoning is not based on matter that is of a type that reasonably may be relied upon by an expert in forming an opinion upon a subject. The bill would define circular reasoning as referring to any portion of an expert's opinion that is solely based upon the premise that the expert seeks to conclude, including any portion of the opinion or testimony that is based upon studies, literature, data, or other materials on which the expert relies that accepts the same unproven premise that the studies, literature, data, or other materials on which the expert relies seeks to conclude.