There are two different auto theft charges - grand theft auto and unlawful taking of a motor vehicle. Both carry the same potential punishment - there are slight differences in the elements and what must be proven.
For grand theft, they must prove he is te one get took the vehicle. For auto theft, they can prove that he either took or drove the vehicle.
For grand theft, they just prove he had the intent to permanently deprive the owner. Adore unlawful taking, hey must prove intent to permanently or temporarily deprive the owner.
Either way, he absolutely needs an attorney. You need a good criminal defense attorney. I'd strongly suggest you find someone who focuses on criminal law and who routinely practices in the court where this case will be heard.
The above answer is for general information only and is based on the information you posted. Every case is fact dependent, so to get a thorough analysis of your situation, you will need to consult face to face with an attorney licensed to practice in the jurisdiction where the incident took place. Do not conclusively rely on any information posted online when deciding what to do about your case.
There is no special scientific scale for how much evidence is enough to put a person in prison. Enough evidence means that the prosecutor convinces a jury of 12 laypeople that your son should be found guilty "beyond a reasonable doubt." "Do they need witnesses?" No. "Do they need fingerprints?" No. "Don't they need some kind of scientific evidence other than his being there?" Really really, there is ABSOLUTELY no requirement for the prosecutor to meet other than convincing twelve people to convict.
Sorry to hear about this. Your son may want to speak to a civil rights attorney if he is found not guilty of the grand theft auto charge. I wrote a short article on what is grand theft auto that should answer all your questions. Because of the crazy force used by police, you may want to think about a Pitchess motion to uncover the police officer's personnel records to see if he or she has a history of excessive force.
There are many different ways for the prosecution to attempt to prove a charge....1) direct evidence such as eye witness ID and 2) circumstantial evidence such as fingerprints. there is also possible statements made by your son or others (co-defendants). I would have to hear all the facts to be more specific. I wish your son well......David Wallin