Illegal Seizures

First of all, more about the circus revolving about local Republicans:

Ex-Knox worker mum on lawsuit: GOP campaign specialist says he was harassed by sheriff's deputies (Knoxville News Sentinel, registration required)

"On Friday, Harber said the incident with the sheriff's deputies, in which he says undercover officers handcuffed him and searched his vehicle without showing him a search warrant, made him fear for his safety."

...

The Sheriff's Office is investigating whether a crime was committed when someone obtained former GOP chairman Chad Tindell's e-mails and provided copies to [Knox County Mayor Mike] Ragsdale.

In his resignation email, Harber said this about fellow blogger Adam Groves:

"Shortly before my incident, Knox County Sheriff Officers invaded my close friend, Adam Groves’ house and conducted an illegal search and seizure of his computer and illegally and forcefully interrogated him while showing no warrant, receipt of property confiscation, and without demonstrating due cause."

However, the allegations about illegal search and seizures of Harber's and Adam Groves' cars, houses and PC's are serious. What I haven't been able to glean from the narratives (and is difficult to find, anyway, in the midst of such hyperbole as "invaded" and "forcefully"), however, is what leads to the conclusion of legality of the actual searches and seizures.

If a law enforcement officer has reason to believe that an item of private property was either used in the commission of a crime, or could provide evidence that the crime was committed by the owner (illegally tapping into Tindell's email system), doesn't the officer have just cause to do so? What kind of legal permission (i.e. search warrants) must be obtained, if any, to allow him to do so? Harber alleges no warrants were presented, yet I'm sure we all know that sometimes the wronged party sees or remembers just what it chooses to, when it's politically expedient. And, to be fair, our men in blue don't always show due dilegence when presenting search warrants, even if they do have them.

I just don't imagine all searches and seizures are "illegal", but have no idea what determines whether it is or not.

Anyone have any ideas?