PORTLAND — The murder trial of Chad Gurney resumed this morning at Cumberland County Superior Court.

Gurney, 29, is charged in the killing of 18-year-old Zoe Sarnacki on May 25, 2009. He has waived his right to a jury and has pleaded not criminally responsible by reason of insanity.

Prosecutors claim Gurney was legally sane when he killed Sarnacki at his Cumberland Avenue apartment.

Justice Roland Cole is presiding over the trial, which opened last Monday.

This morning, an expert witness called by the defense is on the stand. Dr. Harold Bursztajn of Harvard Medical School says Gurney suffered from mood and thought disorders, primarily caused by a 2005 van crash that injured his brain.

Bursztajn testified that those disorders caused Gurney to suffer from intense paranoid delusions.

The trial is expected to conclude later this week.