DNA is inherited from parent to offspring. While new changes occur, a large amount of the DNA between the two are the same, compared to non-related organisms.

DNA is inherited from parent to offspring. While new changes occur, a large amount of the DNA between the two are the same, compared to non-related organisms. This allows us to reconstruct the history, or in cases where there is less data, infer the history of two different organisms. We can roughly tell where, and when one population split from another. In the case of bio-weapons, we can tell if the organism came from a culture in a current laboratory, or if it was generated in secrete. If the latter, we can tell what part of the world the original sample came from. All of this are clues to discovering the culprits. A famous example is the 2001 Anthrax attack in DC. They were able to match the DNA from the anthrax to a US military strain located in Maryland. This led them to a former researcher who most law enforcement believe was the culprit in the attacks.