When scientists James Watson and Francis Crick first mapped the structure of the DNA double helix a half century ago, little did they know that they were also unleashing a powerful weapon in the fight against crime and terrorism.

How powerful? Extremely. Today, DNA evidence and tests can:

So how can DNA do all this? DNA can uniquely identify an individual in ways that even fingerprints can't. DNA is found in virtually every human cell. It can be extracted from hair, teeth, bones, and body fluids (blood, saliva, semen, even sweat!). It leaves traces on everything from cigarette butts to postage stamps, from shirt collars to napkins. And it lasts for years -- even in harsh conditions, even when there's little left of human remains. For example, following the 9/11/01 attacks, investigators were able to find traces of DNA in the rubble of the World Trade Center that identified victims and brought some measure of closure and relief to their devastated families.

But the crime-fighting power of DNA really didn't begin to be unlocked until 1990. That's when the FBI began a pilot project called the Combined DNA Index System, or CODIS -- which, following Congressional approval and funding, became fully operational in 1998.

What's CODIS? CODIS is a three-hitter: computer technology (a database program and software), forensic science (DNA profiles rigorously measured and maintained), and telecommunications (the ability of local, state, and federal labs to share information and communicate electronically) all rolled into one.

Simply put, CODIS stores DNA profiles from around the country in a series of local, state, and national databases, all linked via computers, enabling crime labs at every level to share and compare DNA profiles electronically. Lightning fast searches using CODIS can link DNA found at one crime to other crime scenes and to convicted criminals whose DNA is already on file.

Tomorrow, we'll share more specifics on how CODIS works, talk about how it just passed a significant milestone, and pass on a few recent success stories. Stay tuned!