英语听力：自然百科 揭密联邦调查局 Unit3（在线收听）

Atlanta, Georgia, a terrorist bomb explodes in Centennial Olympic Park, killing one woman and injuring hundreds. North Caldwell, New Jersey, an advertising executive is killed when he opens a mysterious package which explodes in his hands. Oklahoma City, Oklahoma, a powerful blast destroys the federal building, claiming 168 lives. In all three cases, it's a race against time. As an elite division of the FBI known as the Explosives Unit attempts to catch the mad bombers before they strike again.

FBI Explosives Unit is the part of the FBI laboratory. It does the forensic examination of bomb components, unexploded bombs. They also do residue analysis of the explosives that are used in bombs.

Explosives examiner, Donald Sachtleben, agreed to take us inside one of the nation's most secretive crime-fighting laboratories. Here, this team of highly trained technicians and forensic scientists carefully combs through evidence, searching for any clues that will help the FBI capture a bomber. In Atlanta, the search for answers begins at ground zero, the scene of the Olympic bombing where every step is fraught with danger.

At any crime scene, you have to assume that there could be other devices there what we would call secondary devices or booby traps. We've seen that recently in some of the bombings around the Atlanta and Birmingham areas.

In Atlanta, agents are sifting through the rubble of an abortion clinic bombing when suddenly, a secondary device explodes. Miraculously, no one is killed. But seven people are injured, including several federal agents. But in the aftermath of the Olympic bombing, investigators rely on surprisingly common technology to search for deadly booby traps.

The most effective tool that we have is the X-Ray, the portable X-Ray. We can actually go up to a package and with a remote technique; we can put the X-Ray down, X-Ray the package and see whether or not it's a hazard.