Brett and Jeanne Sterling

Brett and Jeanne Sterling, aka Jack and Jill, are the two main antagonists of the Alex Cross book Jack & Jill. The couple are two terrorists and contract killers employed at the CIA, Brett a contract killer and Jeanne working in the position of Inspector General above him. A high-profile client paid them to kill the president, finding them by their aliases of Sam Harrison and Sara Rosen, but outright murdering the man wouldn't be a plan the two killers could afford. They started with targeting official and notorious people, even sending snuff films, to show how serious they are. A senator is the first victim, killed on camera, and once the federal agencies receive the tape, Cross is requested to attend on the case, Chief of Detectives George Pitman personally delivering the news. Cross begrudgingly takes it on despite caring more to fine the "Truth School Killer", Danny Boudreaux. By then, the Sterlings have committed a few more killings. With Cross in the case and the FBI, Secret Service, and CIA all collaborating to form a task force, the Sterlings take an initiative to hire a proxy killer to murder the president, Kevin Hawkins, also for the sake of framing him for the crimes. Hawkins is directed right to the president's mistress to murder her, escaping when Jeanne leads Cross right to Hawkins. Then when the president resumes schedules as planned, Hawkins detonates a bomb in Madison Square Garden, waits at the escape route, and successfully shoots the president dead, taking shots back and dying at the hospital. The duo later kill "Sara Rosen" to throw investigators off, but a tape left behind reveals "Jack". The task force follows Brett and arrests him, revealing him as one of the killers. When Jeanne's given up too, she's arrested after trying to escape. Both die from poison in prison, putting up a resistance when murdered, presumably arranged by the client having hired them to commit the spree.