ATMORE, Ala. (AP) — A man who was paid $1,000 to kill an Alabama woman more than 30 years ago has been put to death with pure nitrogen gas, a first-of-its-kind execution that again placed the U.S. at the forefront of the debate over capital punishment. Kenneth Eugene Smith appeared to shake and convulse before being pronounced dead Thursday at an Alabama prison after breathing the gas through a face mask to cause oxygen deprivation. The execution came after a last-minute legal battle in which Smith’s attorneys said the state was making him the test subject for an experimental execution method that could violate the constitutional ban on cruel and unusual punishment. Smith was one of two men convicted in the 1988 murder-for-hire slaying of Elizabeth Sennett.