In United States v. Van Leeuwen (1970) 397 U.S. 249, a delay of 29 hours to obtain a search warrant, after suspicions were aroused as to contents of the package to be mailed and the sender, was found to be reasonable. Justice Douglas stated that detention of suspicious packages produced by defendant for first class mailing did not constitute an "invasion of the right 'to be secure' in the 'persons, houses, papers, and effects' protected by the Fourth Amendment against 'unreasonable searches and seizures.'" ( Id. , at p. 252.)