The 4th amendment typically applies to police searches involving drug crimes. The 4th Amendment of the Constitution of the United States protects citizens from unreasonable searches and seizures. Heroin Crimes So, when exactly can police search an individual, specifically a person's vehicle? There are several ways a police officer can obtain legal authority to do so. The first is the long drawn out process of obtaining a search warrant. The officer must outline specifically where they will be searching and must provide a reason or justification as to why the search is necessary, and a judge must sign off on the search. However, this is not how most officers obtain legal authority to search an individual's vehicle. Most searches are based on probable case (PC) alone. PC is essentially certain factors are present during an interaction with police that leads the officer to believe a crime has been committed. This gives the officer a reasonable ground to base the search off of. For instance, a very common form of PC is the presence of marijuana odor admitting from the individual's vehicle. If during the course of a traffic stop, the officer detects the odor of marijuana, that officer can use the presence of the marijuana odor as PC and search the vehicle without needing a warrant.