How would you begin to write an argument as to why a traffic stop and all the evidence the officer found should be admissible as evidence if the person who was stopped did not have an active warrant at the time of the traffic stop, but had items in the vehicle that lead the officer to believe the individual was engaged in criminal activity?
The Fourth Amendment to the Constitution of the United States affirms that
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probably cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Many rights explicitly granted under the provisions of the Constitution are regularly subject to interpretation. The Fourth Amendment has been no exception. The authors of the amendment were responding to British colonial practices of allowing blanket searches of homes and businesses on little or no pretext. It was introduced in 1789 by James Madison, and was officially adopted in 1792. It wasn't until 1914, however, with the Supreme Court decision in Freemont Weeks v. United States, that the intent of the Fourth Amendment was finally institutionalized. In that case, the Court determined that warrantless seizures of items from a private residence were inadmissible as evidence in court. The introduction of the automobile during the same period of time added a complicating factor to concepts of privacy and limits on police authorities to search a mobile vehicle and seize items as evidence, but the Court has consistently applied Fourth Amendment protections -- what is known as the "exclusionary rule" -- to privately-owned motor vehicles.
A complicating factor in answering the question, however, arises in that the evidence observed by a police officer during the course of a presumably random traffic stop, and which would logically be associated with criminal activities, for example, burglar tools, suspected narcotics, or certain types of weapons, is not specified as having been observed in plain sight or was discovered in the course of a warrantless search of the vehicle, for example, the trunk or glove compartment of the car, or under a seat. A traffic stop initiated in response to a violation of state code and that results in the seizure of items in the officer's line of sight -- what is known in law enforcement parlance as "evidence in plain view -- is considered a legal action on the part of the law enforcement officer. The 1990 Supreme Court decision in Terry Brice Horton v. California established that "plain view" seizures are admissible in court if the following conditions are met:
First, the objects criminal nature must be immediately apparent; Second, the officer must have a lawful right of access to the object itself; and Third, the evidence must be in plain view.
Similarly, in Warden, Maryland Penitentiary v. Hayden (1967), the Supreme Court decided that property in plain view that an officer recognizes as "contraband or the fruits, instrumentalities, or evidence of criminal activity" may be lawfully seized.
In short, an officer making a legitimate traffic stop -- as opposed to a traffic stop executed for the purpose of searching the vehicle when no warrant exists -- can seize items in plain sight if those items are recognizable as being associated with unlawful activity. Police who stop a car because that car may contain an individual associated with criminal activities, but that was operated in a lawful manner, may not seize objects from that car.
With regard to the seizure of items to be used as evidence that were not in plain view, the requirement for a warrant is paramount.