inspector police. >> they're a major component of this investigation. probably safe to assume they were monitoring, tracking the suspicious parcels after they were informed by the well-trained postal employees around the nation. so they're there because they're part of that team. >> reporter: felix nader was a u.s. postal inspector for 26 years. his concern tonight, even with the arrest of the suspect more bombs could be in the system. >> we are hoping the highly sensitive awareness would put people on queue to be aware and alert of things that might be suspicious. >> te and current postal officials say they have sophisticated screening devices to monitor behavior and elite members of the postal inspector police looking for explosives. >> these dangerous mail investigation specialists are highly proficient in the use of state-of-the-art equipment. >> reporter: what do they look for in dangerous packages? >> certain styles, there's