NEW DELHI: The Supreme Court on Thursday directed the Centre to inform it about the investigation on the aspect of conspiracy behind making of the bomb that had killed former Prime Minister Rajiv Gandhi in 1991.The apex court asked the government about the probe being carried out on this aspect, after one of the convicts in the assassination case claimed that this issue has not been properly probed."What is the result of the re-investigation or further investigation on this aspect? Kindly address us on this. We want only this," a bench headed by Justice Ranjan Gogoi said. The apex court fixed the matter for further hearing next week.Advocate Gopal Shankarnarayanan, appearing for convict A G Perarivalan , told the bench that there were several issues, including the conspiracy behind making of the bomb that killed Rajiv Gandhi, which were not investigated properly in the case.Perarivalan's death sentence was earlier commuted to life term by the apex court in the case.Rajiv Gandhi was assassinated on the night of May 21, 1991 at Sriperumbudur in Tamil Nadu by a suicide bomber at an election rally. 14 others were also killed then. This was perhaps the first case of suicide bombing which claimed the life of a high-profile global leader.