The U.S. Supreme Court will soon decide a case that raises serious questions about the principles upon which American criminal jurisprudence has always rested. Maryland v. King brings us face to face with modern forensic technology and how it can be applied in the criminal justice system without undermining that system.

Police arrested Mr. King for brandishing a shotgun. Under Maryland law, the police were authorized to collect King’s DNA while he was under arrest, but prior to conviction. When Mr. King’s DNA was compared to a database of DNA from unsolved crimes, it was a match for a terrible rape committed in 2003. Mr. King was then charged with the rape, convicted, and sentenced to life without parole. The Maryland Court of Appeals overturned the conviction. A very active U.S. Supreme Court recently heard argument.

The positive side of DNA evidence is well-known. The Innocence Project, for example, has won the release of over 300 people serving time in prison, sometimes for decades, for crimes they did not commit. Only the new science now available can accomplish these laudable releases.

But there is another side to the same technology, one that forces us to consider difficult questions.

The Maryland police had no reason to think that Mr. King was involved in the 2003 crime, or any other crime. Taking the DNA sample was normal procedure in Maryland, as it is in Connecticut where an individual, previously convicted of a felony, is arrested for a serious felony.

Although Maryland’s law does not require the prior conviction that Connecticut’s law does, both raise the same questions: why does the taking of a suspect’s DNA after arrest, but prior to conviction, without prior judicial approval, not constitute an illegal search? What probable cause exists to make these searches consistent with Article IV of the United States Constitution?

When the Supreme Court granted certiorari in Maryland v. King, 49 states, Washington, D.C., Puerto Rico and the Justice Department all filed amici briefs. Justice Samuel Alito commented, "This is the most important criminal procedure case this Court has had in decades."

What is DNA analysis like? Is it the modern equivalent of fingerprinting, as some suggest? Is it different than a fingerprint (which can only be used for identification purposes) and more like a "treasure trove" of deeply personal information, as others suggest? Do you have a reasonable privacy expectation for your DNA when it could be easily obtained from that soda can you just discarded? Is it equally advantageous to society to solve old serious crimes as to free innocent people from prison?

Under traditional analysis, the Maryland police could not have obtained a warrant to extract Mr. King’s DNA to determine whether he was guilty of the crime committed 10 years ago. There was no suggestion of Mr. King’s involvement in that crime.

In its arguments to the Supreme Court, Maryland avowed that the search — conducted by swabbing the inside cheek of the suspect — is only minimally invasive and not unreasonable, and is justified by the government’s need to solve crimes. They stated that one who is arrested has less of an expectation of privacy, based on the conduct that caused his arrest. As a policy matter, Maryland argued that the searches help solve past and future crimes by expanding the DNA database.

But note that the operative word is arrest, not conviction. One could be arrested and be found innocent of the initial charge, but because a DNA sample was taken, be prosecuted for other, entirely unrelated crimes. Has the Fourth Amendment disappeared?

DNA tells a great deal about the person, including sensitive medical information. Are government databases containing this information any more secure than the databases that seem routinely to be lost, stolen, or hacked into, revealing our credit card information and social security numbers to people not authorized to have them?

Maryland v. King asks important questions about our expectation of privacy, the presumption of innocence, and how this technology and others, such as aerial surveillance by drones, fit into our lives. Some of our most treasured constitutional protections may hang in the balance of this decision.•