An interesting aspect of Arizona v Gant  USSC, No 07-542, (21 April 2009) is the omission of any reference to Herring v United States  USSC, No 07-513, (14 January 2009), noted here 15 January 2009.
Gant rejects a broad reading of the Supreme Court's decision in New York v. Belton, 453 U. S. 454 (1981) which had applied an assumption that things in the vehicle were accessible to the person arrested.
The topic is the police power to search a vehicle incident to the arrest of an occupant. Gant holds that the vehicle may be searched when it is reasonable to believe that evidence of the offence for which the person was arrested might be found in the vehicle. It also holds that, since the power of search incident to arrest has the purpose of preventing the arrested person accessing weapons or destroying evidence, the search may only be of areas within the arrested person's immediate control. When the arrested person has been secured and cannot access the interior of the vehicle, a vehicle search incident to arrest is not authorised.
In Gant the search was unreasonable. Mr Gant had been arrested for driving with a suspended licence (or, as they spell it, license) and had been handcuffed and placed in the back of a patrol car. His car was then searched and a bag of cocaine was found in the pocket of a jacket which was on the back seat. The US Supreme Court held 5 – 4 that the Arizona Supreme Court had correctly held that the search was unjustified. That Court had held that the trial court should have suppressed the evidence.
In Herring, the Supreme Court held that the fact that a search was unreasonable does not mean that the exclusionary rule necessarily applies: exclusion depends on whether the efficacy of deterrence of official misconduct outweighs the substantial cost of letting guilty defendants go free. This issue was not argued on this appeal.
One can readily imagine that evidence of a really serious crime might be found as a result of an unreasonable search of a vehicle following the arrest of an occupant for a relatively minor matter. Automatic exclusion would be absurd in those circumstances. The issue of admissibility is distinct from the issue that was argued here – the constitutionality of the search.