A Grand Island man is being charged with threatening a federal drug investigator. U.S. Attorney Deborah Gilg says 18-year-old Alexander Martinez threatened to assault an officer with the Central Nebraska Drug and Safe Streets Task Force on Aug. 6. Court documents say he was trying to impede the task force's investigation. Prosecutors also charged 18-year-old Luis Green-Chavez with helping Martinez avoid apprehension after making the threats. Both are expected to make their initial appearances in court later this week.