After more than three decades in United States prisons — a term punctuated by a brief escape and recapture — a 62-year-old Croatian independence fighter was returned to his native country on Thursday, having served his time for a 1976 hijacking and a bombing that killed a police officer. The fighter, Zvonko Busic, led a group that planted a bomb at Grand Central Terminal that later exploded, killing a city police officer, Brian J. Murray. Mr. Busic left the Federal Correctional Complex in Terre Haute, Ind., boarded a plane in Chicago and touched down in Zagreb about 2:20 p.m. on...