Charges could come as soon as next week in a case reportedly focused on Cuba's downing of two planes in 1996.
Cuba's president faces a number of challenges, including the largest opposition protests in decades.
Miguel Díaz-Canel, who succeeded Raúl Castro as president, will be running the Communist Party.
His resignation ends his family's six-decade hold on power in Cuba.
Raúl Castro has stepped down as first secretary of Cuba's Communist Party ending a 60-year career.
