Vengeance Mine by Chet Cunningham
Someone is killing lawmen, killing them slowly and sadistically. Deputy U,S. Marshall Chance Thorne, assigned to San Diego to catch a couple of bank robbers, is now under orders to find the killer. Convinced by evidence that it's a women he's after, he decides that wearing his badge is the best way to lure her into the open. But will the hunter become the hunted?