RIO DE JANEIRO, Brazil, April 1 (Reuters) - Brazilian police arrested a man on Thursday who confessed to murdering a U.S. oil executive and his wife in Rio de Janeiro four months ago in a crime that had until now mystified authorities. Jossiel Conceicao dos Santos, a caretaker at the luxury condominium in Rio where the Utah couple lived, told reporters he killed Todd Staheli and his wife Michelle with a crow bar because they had mocked him and used racist slurs. "Every time I was working in the neighbor's house they laughed and made fun of me. I became...