OAKLAND, Calif. (KGO) -- Judge Morris Jacobson ruled Wednesday that John Cowell must be mentally examined by an expert selected by the prosecution.
Cowell is accused of stabbing 18-year-old Nia Wilson to death on the MacArthur BART platform last July.
RELATED: Judge to reevaluate if John Cowell competent to stand trial for fatal stabbing of Nia Wilson
The defense attorney for 27-year-old Cowell believes he is mentally unstable and not able to stand trial. The prosecution disagrees.
Cowell has already been examined twice. One expert could not reach a conclusion. The other, according to prosecutors, reached a conclusion that was inconsistent with his own reports.
Prosecutors say they can't go into further details because the findings are sealed. The judge granted their request Wednesday that a mental evaluation be performed by an expert they have attained.
RELATED: Nia Wilson's family frustrated by another delay in John Cowell case
The judge set that evaluation for May 30. He said there will be consequences if Cowell refuses to be interviewed. The judge also said these findings may not be used in the trial over his guilt or innocence. These results will only be used in deciding whether he is competent.
After the judge made his ruling, Cowell asked his attorney, "Does this mean I am going to Napa?"
Tomisha Wilson, Nia's sister, said outside the courtroom that she thinks the question shows that Cowell knows exactly what he is doing and that he is mentally competent.
See more stories and videos on the Nia Wilson case.
Man accused of killing Nia Wilson must be mentally examined again
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