Here is a link to one of the better pieces I have seen on a very interesting topic; law enforcement use of familial DNA. Though it is a bit dated, it presents both sides of this controversial topic, and hits most of the main points well.
Imagine the following: your brother/mother/son has committed a crime for which s/he was convicted and sent to prison. Since every state takes a DNA sample of convicted felons, their DNA is on file. Now, imagine that another crime has been committed, and that the police have DNA of a potential suspect. After sending it to the lab, technicians are able to determine that it wasn't your incarcerated family member, but that the sample is a partial match. In some states, this could lead to the police knocking on your door. Why? It is because partial DNA matches point to familial relationships, meaning that there is a reasonable probability that it was your DNA at the scene.
This may seem like an efficient way to solve crimes, get criminals off the streets, and arrive at just results. These are some of the main arguments utilized by advocates of the practice. However, on the flip side, opponents point to the potential for privacy issues and intrusion into basic civil rights. This side would argue that, although under a social contract framework, a felonious family member may have lost their own privacy rights upon being convicted, it does not follow that every family member has done the same.
The FBI currently has an interim policy in place where states may determine their own policies in using partial, or familial, matches. Some of the most high-profile states pursuing this method include Colorado, California and Massachusetts. The only state with a legislative policy against the practice is Maryland. Most other states fall somewhere in between. And this is part of the problem, according to opponents; a lack of a clear policy makes it nearly impossible to determine which states are doing what, or sharing what information with whom. Much of this is due directly to the FBI's policy, as many states are reluctant to set out a definite course of action barring clear direction from the nation's top cops.
This relatively new crime fighting technique has been used for some time in England with success. Additionally, a quick Google search will also lead to some interesting stories of both cold and recent cases in the States being solved with the help of this technology. However, the inherent privacy concerns should not be lightly brushed aside, and it is both interesting and telling that both the FBI and many states are taking such a hands-off approach to the topic. Until the FBI establishes a definitive strategy, the most likely outcome is that both sides will continue to argue over this contentious topic with both victims of crime and victims of unjustified privacy violations being the ones who truly suffer.