An open letter to U.N. Secretary-General Ban Ki-moon signed by more than 1,000 people, including financier Warren Buffett, U.S. Sen. Elizabeth Warren and rock star Sting, says the war on drugs has failed and calls for a shift in global drug policy from emphasizing criminalization and punishment to health and human rights. The letter signed by former presidents of Mexico, Colombia, Brazil, Switzerland and others, was made public Thursday in advance of a United Nations special session on the topic beginning April 19. It was released by the New York-based Drug Policy Alliance.