It was only a matter of time before it became possible to create fake DNA evidence. That time is now.
DNA Evidence Can be Fabricated [New York Times]
Think it's bad when somebody steals your identity, drains your bank account, and spends thousands of dollars on credit cards they opened with your name on it? This run of the mill identity theft can cost you thousands of dollars, and many years to clean up. It pales in comparison to what will happen if biometric data becomes commonly used as proof of identity. Sometimes also called bio-print (like fingerprint) or bio-identity mechanisms, such things as retina scans and fingerprint scans are already in use, or even common use. DNA scans are likely to become possible several years from now, as the technology to read DNA is evolving rapidly. An entire genome can be sequenced by three people and equipment costing a few hundred thousand dollars, in a very short period of time, several days. When it become possible to read DNA in more or less real time, people will undoubtedly clamor to use it as an identity mechanism, for bank access, for voting, and who knows what else.
Even (or perhaps long, if you doubt that day is near) before that's possible, databases will be filled with your DNA sequences, because it will be valuable to you and your doctor. Unless we get unexpectedly better at protecting data, those databases will be protected by the same organizations, people, and technologies which today fail to protect your simple text based identity -- your name, date of birth, social security number, address, and phone number.
With current technology, you can engineer a crime scene. You can make it look like a specific, innocent person committed a homicide, for example. The technology required to do so remains expensive, but it's well within the reach of governments, and the capabilities of research labs.
If you're writing the next hollywood script for Jason Bourne or James Bond, keep your eye on this stuff. It's moving faster than Hollywood.