A Santa Rosa man who pleaded not guilty by reason of insanity to killing his father can be examined by a doctor hired by the prosecution, a judge ruled Monday.

Two court-appointed psychologists have already found that Houston Herczog, 21, was suffering from paranoid schizophrenia when he stabbed to death Mark Herczog, 63, in their Rincon Valley house in 2011.

A third doctor hired by the defense reached the same conclusion.

But on the eve of trial, prosecutors sought input from their own expert. Judge Dana Simonds granted a request to have Dr. James Missett, of Menlo Park, conduct a series of tests on Herczog.

The ruling came over the objection of Herczog's lawyer and his family, who insist Herczog was suffering from a mental disorder at the time of the slaying.

The trial was scheduled to begin April 5. It was unclear if the additional review would lead to delays.