If he is not competent to stand trial he will be placed in a state hospital until he is. An insanity may not work to reduce the charges as the legal definition of insanity is quite different from the medical diagnosis. He could have paranoid schizophrenia and still be aware of the nature and quality of his acts. That said this possible defense needs to be explored with doctors who work in the field of sexual disturbances.
This is far too complicated to adequately cover in a public forum. I would suggest meeting with several attorneys who offer free consults and see what you learn from there.
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California does not have a diminished capacity defense anymore. However, mental illness can negate the specific intent necessary for some crimes. You should discuss the particulars of your brother's case with a lawyer, face to face.
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You should consult with a local lawyer in a private setting to share additional facts regarding this matter. I would need to know if your brother has a prior record and the facts surrounding the misdemeanor charge to assess this case. In various types of battery cases, lesser included charges can be negotiated with good investigation and lawyering. However, lawyers cannot guarantee a better outcome when they take on representation.
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