A Haitian-born doctor based in Florida has been arrested as a key suspect in the assassination of President Jovenel Moïse of Haiti, and the national police chief suggested at a news conference that he believed the suspect was plotting to become president. To date, some two dozen people have been arrested in the killing, but on Sunday, Haitian officials described the doctor, Christian Emmanuel Sanon, 63, as a central figure in a case. Even as the Haitian authorities offered their most detailed account so far of the plot behind the brazen assassination of the president in the bedroom of his private home last week, there was widespread skepticism among the public of the official version of events.