DNA is miracle evidence in court. It can solve long-forgotten “cold cases,” and it can overturn verdicts reached by a unanimous jury beyond a reasonable doubt.

It seems that there is no limit to what the science of identification can do, unless we as a society put limits on it ourselves.

That’s just what the U.S. Supreme Court is considering, and this is one case that is not likely to break down on the usual ideological grounds. There is a legitimate difference of opinion about whether DNA is just an incremental improvement in gathering evidence in crimes, or if it represents a new level of intrusion that can violate the constitutional protection against unreasonable search and seizure.

There is no easy answer here, but this is a case where the court should err on this side of caution. It would be better to let a guilty person go free than to subject anyone who the government wants to surrender evidence against themselves.

The case involves a practice carried out in all 50 states: collecting DNA samples from people arrested but not convicted of a crime. DNA profiles can be run through a national database, potentially connecting the donor to previously unsolved crimes. And the profile will forever be among the known samples that will be checked against DNA found at crime scenes.

The practice is described as “21st-century fingerprinting.” For a century, law enforcement has collected fingerprints. Sometimes they are used to solve crimes, but their primary purpose is to identify the people in custody.

Ostensibly, that’s why they collect DNA, but it can do so much more. The information it contains can be kept for a lifetime and can be used to solve crimes that have not yet occurred.

We are all for catching the guilty, but as Justice Antonin Scalia pointed out last week, sometimes the Constitution gets in the way.

People under arrest have less privacy than those who are not in custody, but merely having been accused should not be enough to open someone’s whole life to added scrutiny. Having been convicted of a crime should be the threshold before one can be compelled to provide a DNA sample without a court order.