Supreme Court Justice Dipak Misra who had rejected Mumbai blasts convict Yakub Memon's mercy plea has received an anonymous threatening letter. Delhi Police have registered a case in this regard and have started an investigation. A three-judge bench of the Supreme Court had unanimously rejected Yakub Memon's petition seeking stay of his execution, putting an end to last-gasp efforts to help the 1993 Mumbai serial blasts convict escape the gallows on his 54th birthday.