When Charles Parker registered as a sex offender in the small upstate town of Jonesville, S.C., he became a prospect on another man’s kill list, the authorities say.

Mr. Parker, 59, died this week at his home, shot in the neck and chest and then stabbed. His wife was also shot and stabbed.

Sheriff’s officials believe that the double murder in Jonesville, a one-square-mile town of about 900 residents, was not the byproduct of a botched drug deal or a home invasion. Rather, they suspect that Mr. Parker’s death was intended as the opening phase of a man’s quest to purge sex offenders from Union County.

“He went through our sex offender registry,” said Sheriff David H. Taylor, “and individually picked out targets.”