They can secure property in order to get a search warrant if they think evidence will be otherwise destroyed.
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Except the dirt and cracker crumbs part, sadly for you this all sounds kosher to me.
If law enforcement has an arrest warrant and sees the subject of that warrant in a car then they can lawfully stop the car and detain the driver while they serve the warrant and arrest the subject. If, in the process, they observe criminality (i.e. weed in the car) then they can act upon that as well.
While police generally cannot search a car without a warrant or consent there are exceptions (for example, in your case, they may have been authorized to do so as either incident to making the arrest or if they had reason to believe that either you or the subject was armed and dangerous and therefore needed to do a protective sweep for officer safety).
Once an arrest is made all property belonging to the arrestee should be impounded, properly labeled and stored. If law enforcement wished to gain entry into any impounded property (be it a cell phone, a suitcase, a laptop or vehicle trunk, whatever), then they can maintain possession and control over the same for a reasonable amount of time while they attempt to secure a search warrant. While officers have discretion to return property to someone instead of impounding it (for instance, you get pulled over and arrested for DUI but the cops allow your wife to come get the car instead of causing it to be towed it away) they are under no obligation whatsoever to do so.
It sounds tome as though a) your friend is in some hot water and b) you may have a defendable case yourself. As to each of you I suggest that you make appointments with a St. Cloud area criminal defense lawyer, show-up on time, engage in a meaningful Q&A and determine how to proceed in your best interests.
Although I practice primarily in Miami-Dade County you are welcome to contact my office for a referral or two, or you can search do a location search here on Avvo or you can search the Florida Association of Criminal Defense Lawyers website by locality (please see http://www.facdl.org/ - and click on the "Find A Lawyer" tab).
Either way, best of luck!
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