Does the FBI's use of a fake cell tower constitute an illegal search?

They set up this tower to capture information on a suspect in a fake ID ring that was forging IRS tax returns, netting them $4 million in three years. The suspect is defending himself in court ("...has a fool for a client") and demands information on this device known as a Stingray. Part of the issue is that it captured everyone's voice/SMS/cell data traffic before passing it to an actual cell tower, so they were capturing far more than just the suspect's information.

http://www.wired.com/threatlevel/2011/11/feds-fake-cell-phone-tower/