Party's State unit President Tamilisai Sounderrajan also charged the government with not taking a "firm decision" when there was time earlier.
Speaking to reporters here, she underlined her party's stand that not a single culprit should be spared while no innocent should be punished.
"One has to take a humane approach while looking at the time spent by them (the seven convicts) in jail but everything should be within the legal framework," she said after paying obeisance at the Lord Venkateswara Temple here.
DMK President M Karunanidhi had also backed the decision, saying the convicts had spent about 25 years behind bars.
Former Prime Minister Rajiv Gandhi and 14 others were killed on May 21, 1991 when a suicide bomber blew herself up at an election campaign rally in Sriperumbudur, near Chennai.
