There is a process to the criminal court. A person is not automatically found guilty of a crime and sentenced. There are many hurdles and protections given to each and every person through the United States Constitution so that their rights are protected.
When a person has been arrested, they are arrested based upon the officer’s observations and Judgment. This does not mean that a person has been charged. The officer will prepare a report that essentially states the reasons they believe a person should have been arrested. They must also state the reasonable cause they had to make the arrest in the first place. Once this has been completed, the officer will give their evidence and report to the Prosecutor’s office.
The Prosecutor’s office is aware of the elements that they must provide beyond a reasonable doubt in order to find someone guilty of the offense they have been charged with. For example, for a person to be found guilty of driving under the influence in Los Angeles, they must show that 1) the person was driving and 2) the person was intoxicated at the time they were driving. Both elements must be proved beyond a reasonable doubt. If the evidence is weak, or does not support such a conclusion, Prosecutors will not waste resources and will not formally charge the person.