1. The body never should have left Dallas and the autopsy should have been done in Dallas. That is the law, period.
Legally speaking, this is accurate. However, it alone does not indicate a conspiracy. Emotions were running high after the President was assassinated and the Kennedy people (along with Johnson people) wanted to get back to Washington. Johnson wasn't going to leave without Jackie and Jackie wasn't going to leave without the body of her husband. There were also security concerns that someone would make an attempt on Johnson's life.
The autopsy should have been done in Dallas, however, there were other issues occurring at the time that must be considered. In this instance, it appears that emotion and fear outweighed the law.