The President was only doing his job by granting state pardon to some convicts. But, he unknowingly stirred the hornet's nest. Some queried the rationale for his action, wondering why pardon was granted to Herbert Macaulay and Maryam Sanda, especially. As the President, he has the power to exercise the prerogative of mercy. It is not about justice which had already been served, but about the constitutionality of his action, which is beyond reproach.
According to the Bible, "mercy triumphs over judgment". The President did not quash the courts' judgments, he only had mercy on convicts who had served part of their punishment. As Shakespeare wrote: "the quality of mercy is not strained; it drops as the gentle rain from heaven upon the place beneath. It is twice blessed: It blesses him that gives, and him that takes".
It is the prerogative of the President to do what he deems fit. God put it this way: "I will have mercy on whom I will have mercy..." It is easy to criticise these things when the shoe is on the other foot. Ask Maryam Sanda's father-in-law who has been pushing all these years for her pardon despite being convicted for killing his son, who was her husband.