As much as I lean toward prosecution over criminal defense, let me relay a story told to me by a defense attorney when asked why he defends accused criminals -
A young man and his sister were attending a party and he had too much to drink. He did not remember leaving the party. On the way home there was an accident and the sister was killed. When found by a passer-by, the car was upside down and both people were partially out of the car. The witness helped remove both people from the car but she was already gone. The witness tells police he observed the boy on the left side of the car so he was arrested and charged with intoxicated manslaughter. Facing 20 years in prison he pleaded not guilty and went to trial all the while convinced of his own guilt and despondent over killing his sister.
On the witness stand the person that found them was being cross examined by the defense (cutting this shorter here) and eventually got exasperated. In frustration he affirmed that, yes the boy was on the left side of the vehicle. The defense attorney asked if he had witnessed the accident occur to which he said No. "Then how do you know he was driving?" he was asked - his response - "I never said he was driving. What noone has bothered to notice, or let me explain, was that the car was UPSIDE DOWN. Therefore, the "left" side of the car was the passenger side."
The boy was not driving. He did not kill his sister. He was himself convinced of his own guilt but he was wrong. Without a defense attorney, he would have gone to prison for his sister driving drunk.