avoid repeatation of history

during the last week, a new question has arisen on Indian Politics, that the no. of petitions were pending before the president's office, including that of those responsible for the assassination of former prime minister Rajiv Gandhi for seven years, that of Afzal for a little over one year and so many of others . The president of India has to decide whether the punishment imposed by the Supreme court i.e. highest apex court in the country, is to be implemented or not? We can't understand on which ground these mercy petitions are dealt with?Even though the constitution have accorded the powers to the president, these are to be reviewed from the point of terrorism. There is no system to recheck the evidences at Prez level.Moreover a huge money and time of all the executive as well as judiciary system is incurred to reach up to the final decision. The money is paid by all the tax payers all over India.Then why the delay or the rights to show the mercy on these culprits, to whom all the opportunity was given to justify their dirty works.It is feared that some of the terrorist group may again try to black mail the India, by hook or crook to release these terrorist. It happened in India once. The question is why we are not learning from the History and try to avoid the mistakes repeatedly.