LE can't just get search warrant right away , they have to have probable cause and then prove to the judge. Alot of times they have to be specific on what they are after and it takes time. Here is some info for search warrants:
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Under the Fourth Amendment to the United States Constitution, most searches by the police require a search warrant based on probable cause, although there are exceptions. Any police entry of an individual's home always requires a warrant (for either search or arrest), absent exigent circumstances, or the free and voluntary consent of a person with reasonably apparent use of or control over the property. Some commonly cited exigent circumstances are: hot pursuit of a felon (to prevent a felon's escape or ability to harm others); imminent destruction of evidence before a warrant can properly be obtained; emergency searches (such as where someone is heard screaming for help inside a dwelling); or a search incident to arrest (to mitigate the risk of harm to the arresting officers specifically).[1]
Under the Fourth Amendment, searches must be reasonable and specific. This means that a search warrant must be specific as to the specified object to be searched for and the place to be searched. Other items, rooms, outbuildings, persons, vehicles, etc. may require additional search warrants.
To obtain a search warrant, an officer must first prove that probable cause exists before a magistrate or judge, based upon direct information (i.e. obtained by the officer's personal observation) or hearsay information. Hearsay information can even be obtained by oral testimony given over a telephone, or through an anonymous or confidential informant, so long as probable cause exists based on the totality of the circumstances. Both property and persons can be seized under a search warrant. The standard for a search warrant is lower than the quantum of proof required for a later conviction. The rationale is that the evidence that can be collected without a search warrant may not be sufficient to convict, but may be sufficient to suggest that enough evidence to convict could be found using the warrant.
US police do not need a search warrant to search a vehicle they stop on the road or in a non-residential area if they have probable cause to believe it contains contraband or evidence of a crime.[citation needed] In that case, police may search the passenger compartment, trunk, and any containers inside the vehicle capable of holding the suspected article. By comparison, under Australian law, police can exhaustively search any vehicle on a public road, and any electronic devices therein (mobile phone, computer), without the responsible persons' permission, for evidence of criminal acts, with or without proof or suspicion of any kind.
Police do not need a search warrant, or even probable cause, to perform a limited search of a suspect's outer clothing for weapons, if police have a reasonable suspicion to justify the intrusion - a Terry 'stop and frisk.'
In the United States, the issue of federal warrants is determined under Title 18 of the United States Code. The law has been restated and extended under Rule 41 of the Federal Rules of Criminal Procedure. Federal search warrants may be prepared on Form AO 93, Search and Seizure Warrant.[2]
Each state also promulgates its own laws governing the issuance of search warrants.
http://en.wikipedia.org/wiki/Search_warrant
