A senior Clinton Administration official tellsTIME Miami bureau chief Cathy Booththat the U.S. has "serious concern" thatHaitian President Jean-Bertrande Aristide's interior minister, Mondesdir Beaubrun, may have been involved in the assassination of Mireille Durocher Bertin , a political opponent of the president, on Tuesday. "There are some real thugs still involved as Aristide supporters on the left and they're settling accounts from the past," the official said. The matter has taken on political urgency because President Clinton plans to visit Port-au-Prince on Friday -- the first U.S. president to do so in 60 years. Booth reports that an FBI investigation has "apparently implicated" Beaubrun, whom the Haitian president had appointed over U.S. objections to pacify army supporters. But, the Administration official adds, "There is no reason to believe that Aristide is involved or knew about it."