In general, it is recommended you rely on your police training of maintaining your composure while assessing the overall situation. In particular, maintain a calm exterior presence. Noise or movement can increase the escalated behavior, it is best the area be cleared of bystanders to allow the individual with autism to calm down. If at all possible, contact someone familiar with the individual to gain particular insights in the best means of allowing them to calm themselves. Autism was initially misdiagnosed and treated as a mental disease or a psychological disorder thought be to be brought upon by parental neglect or abuse.
Autism is a broad spectrum neurological disorder.
Advise the family or care providers, if appropriate, information and assessments are available. There is no readily available answer. The increase in number of diagnoses have prompted an increase in research activity but to date there is no consensus of opinion as to the cause or causes. There is some evidence of it being a genetic disorder while other sources of brain injury are suspected e.g. chemical or biochemical toxicity, allergic reaction, exposure to certain viruses. No, but persons with autism may have, or may develop, a mental disease just the same as anyone in the general population.