On Saturday, he and his wife were found shot to death in their rural home just outside the town of Forney, about 20 miles from Dallas.
While investigators gave no motive for the killings, Forney Mayor Darren Rozell said: "It appears this was not a random act."
"Everybody's a little on edge and a little shocked," he said.
The slayings came less than two weeks after Colorado's prison chief was shot to death at his front door, apparently by an ex-convict, and a couple of months after Kaufman County Assistant District Attorney Mark Hasse was killed in a parking lot a block from his courthouse office. No arrests have been made in Hasse's slaying Jan. 31.
McLelland, 63, is the 13th prosecutor killed in the U.S. since the National Association of District Attorneys began keeping count in the 1960s.