The legal system of the United States owes much to the English common law from which it descended. And long before the Fourth Amendment to the U.S. Constitution and its noble statement of the "right of the people to be secure in their persons, houses, papers and effects," the spirit animating the amendment had already been expressed in a famous adage: "An Englishman's home is his castle."

In the American reiteration of an individual's private refuge against official intrusions, that right has been extended to other places and situations. But does a person's constitutional expectation of privacy extend to the jailhouse or booking center, which is less like home than a cell in the allegorical castle?

U.S. District Judge David S. Cercone thinks it does. In a case that brought an ancient principle to bear on the modern technology of DNA, the judge ruled that a defendant indicted on a drug charge -- but not yet convicted -- cannot be compelled to give up a DNA sample as required by law. Without a warrant or reasonable suspicion, the judge said, such sample taking intrudes on the defendant's expectation of privacy and is invalid under the Fourth Amendment.

Judge Cercone's opinion was carefully argued. Indeed, to read it is to be gratified that the federal bench in Pittsburgh has a judge so sensitive to protecting the rights of the people under the Fourth Amendment. But in the end, his legal analysis fails a straightforward test of logic. If fingerprints can be routinely taken from defendants, it seems clear that seeking DNA, a tool that has taken law-enforcement beyond fingerprinting, should also pass constitutional muster.

Judge Cercone dismissed the fingerprinting comparison as "pure folly." He said it ignored "the complex, comprehensive, inherently private information contained in a DNA sample" -- such as family lineage or predisposition to disease. But such data is not what law enforcement seeks or cares about, and the taking of a swab of cells or a blood sample is hardly an imposition on individual dignity.

The judge also sees the use of DNA as an investigative step going beyond the normal identification done by fingerprinting. But when a person is arrested, it is reasonable for the police to check whether someone they think is guilty of one crime might have left evidence of guilt in others. In this case, the defendant had been convicted earlier of other crimes, a fact that naturally gives rise to suspicions.

DNA has been a modern blessing in the securing of justice, convicting the guilty and exonerating the innocent. If police were randomly testing people, the Fourth Amendment would be offended. But those who have been arrested are in a different category altogether. This decision ought to be overturned on appeal.

Cartoonist Rob Rogers does "Rob's Rough," an early look at his work and his creative process, exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.