From the late 1970s through 1986, a vicious criminal terrorized California with 12 murders and more than 40 rapes. In late April, police in Sacramento arrested Joseph James DeAngelo, 72, charging that he was the Golden State Killer, the Original Night Stalker and the East Area Rapist.

By some accounts, DeAngelo was the most prolific criminal to avoid capture. DNA was crucial to the arrest, and victims and relatives alike expressed relief that their nightmares were over. Even so, some journalists were raising concerns that DNA itself might pose a threat.

The Golden State Killer’s murder victims included Keith Harrington, 24, and his wife, Patrice Harrington, 27, who was also raped in the 1980 case. As Keith’s brother Bruce Harrington explained, when DNA kicked in as a crime-solving tool, he urged the Senate Public Safety committee to establish a DNA database but “ran into a buzz saw of opposition.”

Harrington backed 2004’s Proposition 69, which allowed DNA testing for felons. The measure passed despite furious opposition from the ACLU. It came up again after the arrest of DeAngelo.

“If there’s anything to be cautious about,” wrote Erika Smith of The Sacramento Bee, “it’s the collection and storage of genetic material from thousands, if not millions, of people.” For the paper’s Stuart Leavenworth, the tactic of DNA matching “has put genetic testing companies on the defensive and raised questions about their ability to protect consumer privacy as investigators increasingly seek out DNA databases to solve crimes.

Police got DeAngelo’s DNA from the rape kits. Then they got more from objects he discarded after they identified him through a relative who left a sample on GEDmatch, an open source database.

Those concerned with privacy should not entrust their DNA to sites that offer no security protections, but such people would do well to keep the potential benefits in mind. As Bruce Harrington pointed out, DNA helps law enforcement apprehend violent criminals but also helps to clear those unjustly accused.

DNA is a matter of science, not conjecture. DNA does not lie or change its story. DNA suffers no sudden loss of memory, and has no need to plead the Fifth Amendment. The value of DNA as tool to convict the guilty and clear the innocent outweighs the concerns over privacy.

Those who oppose its use in law enforcement can rightly be accused of being anti-science and elevating the rights of criminals above those of innocent victims. That is common practice in California, where Proposition 47 has downgraded felonies to misdemeanors and Proposition 57 gives convicted double murderers a second hearing with no need to present new exculpatory evidence.

Beyond DNA, the case against DeAngelo raises another constitutional issue. In 1977, when the East Area Rapist was racking up victims in Sacramento, gun stores practically sold out and many of the buyers were women. “I’m going to learn to defend myself,” one woman told reporters, “I am getting tired of being scared all the time.” As another woman said of her .38 revolver, “I wouldn’t hesitate to use it.”

Those women knew that if the East Area Rapist comes after you, nothing is a match for a “good blaster at your side,” as Harrison Ford said that year in Star Wars. And there’s no denying that rapists and murders are still on the prowl.

Mr. DeAngelo will get his day in court, DNA and all. In the meantime, all potential victims should disregard the opinion of former Supreme Court Justice John Paul Stevens that the Second Amendment is a useless relic. And everyone should remember the old adage: Better to be judged by twelve than carried by six.