AFTER four years of investigations, the Rajiv Gandhi assassination remains a mystery. The Special Investigation Team (SIT) headed by D.R. Kartikeyan has managedto nail only the third-rung operators in the conspiracy because of the series of slip-ups in the course of the probe. While loose ends were not tied up, important leads were not followed up. The main accomplices of the assassins could not be caught alive and some of the major conspirators were not charged "for want of evidence". And so, a case which the SIT chief had dubbed as "one of the most transparent cases in the world" seems to be making, to quote Sonia Gandhi, "tardy progress".