The observations of the police officers and witnesses, who actually see the suspect's conduct and condition at the time of the offense, often provide the greatest insight into the defendant's mental state. The officer should be alerted to conditions which could indicate a defense of diminished capacity (i.e., bizarre conduct, extraordinary violence, the presence of drugs or alcohol, abnormal emotional response, or unexplainable actions). Specific suggestions are made to obtain a prearraignment psychiatric examination and samples of the suspect's body fluids and handwriting. These suggestions are accompanied by advice on how these may be regarded in court (i.e., whether evidence obtained by these means is considered testimonial or nontestimonial). Written detailed officer observations concerning certain odors, the suspect's reaction to light, and the suspect's manner of speech and coordination are all strongly advised. These all help to determine the presence of toxic substances and could indicate substance abuse. Both field sobriety tests and the gathering of background information which could indicate the presence of a prior history of aberrant conduct are also suggested. A discussion guide, a three-question quiz, and one suggested reference for further reading are provided.