A man convicted of killing two convenience store employees in a 1989 robbery was executed by the state of Arizona after he lost an appeal that raised questions about the drugs used in putting him to death by lethal injection. A jury convicted Eric John King in 1990 of two counts of first-degree murder in the shooting deaths of convenience store clerk Ron Barman and the store's security guard, Richard Butts, during a robbery that netted the killer $72. King, 47, was executed at a state prison in Florence, Arizona, southeast of Phoenix, according to state Attorney General Tom Horne....