The silver platter doctrine is an old legal doctrine on the issue of when evidence can be used in court even if it has been found in an illegal search or seizure. This doctrine is obsolete today, having been overturned by the Supreme Court of the United States in the case of Elkins v. United States which was decided in 1960. The silver platter doctrine said that US government officials could use evidence that had been obtained illegally so long as it had been obtained by state officials without any federal involvement. It was called the silver platter doctrine because the idea was that the state officials had to give the evidence to the federal officials on a silver platter, without the federal agents having to do anything to get it.
This doctrine has now been thrown out by the Supreme Court because it seems to give the federal officials an incentive to connive with state officials in illegal searches and seizures. Thus, the silver platter doctrine is no longer in effect.