Any expert my still rely on hearsay in forming an opinion, and my tell the jury in general terms that he did so.
People v. Sanchez (2016) 63 Cal.4th 665, 685, emphasis in original.
What an expert cannot do is relate as true case-specific facts asserted in hearsay statements, unless they are independently proven by competent evidence or are covered by a hearsay exception.
Sanchez 63 Cal.4th at p. 686, emphasis added.
Experts may rely on inadmissible hearsay. If the hearsay is general background information, experts may relate (repeat) that background information.
If the hearsay is case-specific (involving the particular facts or participants in the case), experts may generally describe the sources of information, but may not relate specific facts, unless (1) the expert has personal knowledge of those facts, (2) the facts are established by other evidence, or (3) the case-specific hearsay falls under a hearsay exception.