When the government wants to conduct an investigation against an individual, it is limited by the Fourth Amendment. This is true whether an investigation takes place in California or any other state. An individual also has a right against unreasonable searches or seizures when a private person or entity is working with a government entity. The amendment applies in both state and federal cases as per a Supreme Court ruling in the case of Wolf v. Colorado.
It is important to note that the Fourth Amendment only applies if a person has a reasonable expectation to privacy. Anything that is submitted to the public can generally be a part of a search or seizure even if the exposure occurred in a private location. Conversely, something could be considered private even if it was taken into a public location. Generally speaking, a person has an expectation to privacy if something is on his or her body or in his or her clothes.
However, if an object is in plain view, it is considered to be in the public domain. This is true whether an object is on a person's body, in an individual's car or in his or her yard. Those who do not own a home or car that is being searched generally cannot object to the search based on the Fourth Amendment.
Anyone who is facing criminal charges may be able to contend that his or her rights were violated by the police or other government authorities. An attorney may argue that evidence was collected in violation of the Fourth Amendment or other applicable laws. A judge may throw out evidence collected illegally, which may weaken the case against an individual. Ultimately, a case may be thrown out before a jury gets a chance to decide a defendant's fate.