It's one thing to take DNA samples of those convicted of a felony. It's another to take it of all persons arrested, according to a lawsuit filed by the ACLU in federal court in California today.

The ACLU says DNA sampling is different from the compulsory fingerprinting upon arrest that has been standard practice in the U.S. for decades. A fingerprint, for example, reveals nothing more than a person’s identity. But much can be learned from a DNA sample, which codes a person’s family ties, some health risks, and, according to some, can predict a propensity for violence.

What’s more, in California the authorities are allowed to conduct so-called “familial searching.” That is when a genetic sample does not directly match another, so authorities start investigating people with closely matched DNA in hopes of finding leads to the perpetrator.

The complaint is here (pdf). A summary of the law being challenged, Prop 69, is here (pdf). Here's a congressional study saying the courts haven't fully addressed the issue and discussing 4th Amendment implications.