You know the drill; through rain, sleet, snow and hail. Every one associates that saying with the Post Office and while its on a building, it's not an official motto and hasn't been used in ads in decades.

Lots of people also think the Post Office operates on tax dollars, also not true. But what is true, is the Post Office has a forensics lab and when a suspicious device is found in the mail, a specialized team disassembles the device.

Check this out, the video shows a reconstructed suspicious device containing nails found near a collection box in Arizona.

"When you have an explosive device, you don't want to move it at all, you want to make sure that it is kept safe, then rendered safe, which means basically disassembled, " explains Forensic Chemist Vincent Desiderio.

Once it is rendered safe the evidence comes here to the Postal Inspection Service's Forensics Lab in Washington, DC. Their mission: to find evidence that will assist investigators to track down a suspect or build a case.

Desiderio handles what's known as trace evidence, that may be any small or minute particle that transfers between an item from one object to another. Since the suspicious package was disassembled for safety, the lab then reconstructs it to examine what is left behind.

For example: they couldn't find any full fingerprints, but they did find a partial inside a box flap. They were able to develop a partial DNA profile of the suspect inside the box. "DNA is very sensitive right now, so you don't need that much in order to get a partial profile."

Piece by piece, the work done in this lab assists in shrinking a list of suspects on that profile.

"I found some green paint inside the box that was associated with some of the components that, the house of the suspect had green decking all around the house."

Then once investigators were able to search the home, they found evidence linked to the return address. It had been photocopied and then handwritten over. This discovery of the evidence made the case.

In the suspect's residence, he had some photocopies and actually an original mailing that had handwriting with the same return address. The suspect in this case was convicted of mailing a dangerous device and got a seven-year prison sentence.

"There is no typical case. That's one of the things that I love about this job is that every case is different."