The hearsay rule prohibits the introduction of out-of-court statements offered to prove the truth of the matter asserted. An expert witness can testify based on hearsay evidence if it is commonly relied upon by experts in their field. The plain view doctrine allows police to seize evidence without a warrant if they see it in plain sight during a lawful search or arrest. Three approaches to determine if plain view applies are: 1) was the initial intrusion lawful? 2) was the discovery inadvertent? 3) was the incriminating nature of the evidence immediately apparent?