Legal Question in Criminal Law in California

The officer needs to have a reasonable suspicion that the person is under the influence. The reasonableness of the suspicion would be determined by all of the factors known to the officer.

Some officers have specialized training as a Drug Recognition Expert (DRE), but that would only be one factor in determining whether the officer's belief is reasonable.

For example, I am not a DRE, but based on my experience as a criminal defense attorney, I can often tell whether someone is under the influence of a central nervous system stimulant, like methamphetamine, or a depressant, such as heroin.

By the same token, a court would consider an officer's training and experience in determining whether an arrest or detention was reasonable.