DNA are allegedly microscopic organisms that reside within the cells of some living things and bestow special powers on those who have them.
The main power they give is protection from receiving the death penalty for murder. This is how they got their name (Death penalty Negating Agents). Sometimes (about 20% of the time), an expert DNAist is able to find an appropriate person to blame for the murder who doesn't have DNA.
Stephen Colbert has DNA, but you can't assume that you do unless you get an expert to check.
More recently, the government has begun a scheme to extract the DNA from all potential murderers (that's everyone!) to make sure that nobody can escape the Death Penalty.