US v. Christian, No. 12-10202 (4-17-14)(Fisher with Berzon; partial dissent by Alarcon). 

The 9th vacated two counts of sending threats via email because the district court precluded the defense expert from testifying about diminished capacity.  The defendant emailed threats to the chief prosecutor of North Las Vegas after the office could not help the defendant in allegedly retrieving his car. The expert, a psychologist, had examined the defendant for competency.  The district court focused on the purpose for preclusion; the court should have examined the substance, which was that the defendant suffered from extensive psychosis and delusions and had difficulty forming intent.  A court must look at the medical diagnosis and not opinions.  The court should have, at the least, allowed defense counsel to voir dire the expert to get the diagnosis out.  The convictions were vacated.  The 9th held too that the court did not abuse its discretion in not instructing the jury on diminished capacity absent expert testimony.  There was evidence of the defendant being disturbed but the evidence was not sufficient for an instruction to find an abuse of discretion.  Alarcon dissented, arguing there was sufficient evidence to require a diminished capacity instruction. 

Of special note is the extension of a civil trial rule, Estate of Barabin v. AstenJohnson, Inc., 740 F.3d 457 (9th Cir. 2014)(en banc) to criminal matters.  In Barabin, the 9th held that erroneous admission of prejudicial expert testimony requires a new trial.  Conversely, applying the reasoning to the criminal context, the erroneous preclusion of expert testimony requires a vacation of conviction and a remand for a new trial.  Barabin applies here.