You'd be surprised at how easy it is to spot an arrest-able offense following the average driver for less than a mile. Just crossing over a pavement paint stripe or stopping past the line at an intersection is "disregarding a traffic control device" and an arrest-able offense. Not turning your turn signal on a minimum of 100' prior to the turn...
The fact that the CNN story says they were arrested for speeding just points to the sloppy and likely biased reporting and lack of facts. If they truly had been arrested for speeding, the plaintiffs' class action civil suit would already have been settled for a tidy sum.
Police said he was driving 37 mph in a 35 mph zone. They hauled him off to jail and threatened him with money-laundering charges -- but offered to release him if he signed papers forfeiting his property.
If they used some other charge under which it is legal to arrest as stated in my first paragraph, well...after that, it's a matter of discovering contraband not as a result of a warrant less search, but as a result of a policy mandated "inventory" of the vehicle's contents ostensibly for the protection of the arrestee's property during the impound process.
All perfectly legal, and all perfectly susceptible to abuse. I don't think it happens often, but it does happen.
And there's no excuse for departments to allow it any more, considering how cheap mobile video systems are these days. If Greenville had them in 1993, even a department with a town pop of 1,000 should have them in 2009.
But I'm still waiting to see more facts about this case. It's still all hearsay and opinion in the news stories on it so far.