By Suchitra Mohanty and Aditya Kalra
NEW DELHI (Reuters) - Yakub Memon's chances of avoiding the hangman's noose for his role in the 1993 Mumbai bombings dwindled on Wednesday, after India's Supreme Court threw out his final plea for mercy hours before he was due to be executed.
Unless President Pranab Mukherjee intercedes, Memon will go to the gallows by 7 a.m. (0130 GMT) on Thursday, his 53rd birthday, for his role as the "driving spirit" in a series of bombings that killed at least 257 people.
The case has aroused controversy because police considered Memon's brother, "Tiger" Memon, and mafia don Dawood Ibrahim to be the masterminds behind attacks designed to avenge the destruction of an ancient mosque by Hindu zealots in 1992.
Both men remain in hiding.
While the public backs Memon's execution, several lawmakers and retired judges have come out in his support, saying the sentence is too harsh in light of the help he gave investigators in cracking India's deadliest bomb attack case.
Calls for reprieve grew after a website last week released a 2007 article by intelligence official B. Raman, who coordinated Memon's arrest in 1994, and said the prosecution appeared to have failed to highlight mitigating circumstances in its eagerness to secure a death penalty. Raman has since died.
A three-judge Supreme Court panel rejected Memon's last-minute petition, clearing the last judicial barrier to his execution, due to be held in a jail in India's western city of Nagpur.
"The issuance of death warrant is not illegal and thereby we don't find any merit in the convict's petition," the panel said, dismissing Memon's petition before a packed courtroom.
Memon's lawyer, Raju Ramachandran, urged the court to commute his punishment to life imprisonment, saying he suffers from schizophrenia. Ramachandran declined to comment after the hearing.
The governor of the western state of Maharashtra, whose capital at the time of the bombings was still called Bombay, rejected an appeal for mercy, leaving the final say on Memon's fate to President Mukherjee.
Rights group Amnesty International, which campaigns against the death penalty, has previously called the rejection of Memon's appeal a "disappointing and regressive step".
Despite India's long-held reluctance to carry out death sentences, it voted against a U.N. draft resolution calling for a global moratorium on executions in 2012.
In November 2012, India executed a militant convicted over a 2008 attack by militant gunmen on Mumbai's landmark Taj Hotel and other targets in which 166 people died, ending what many had seen as an undeclared moratorium on capital punishment.