"We have not considered the nature and character of the accused who were sentenced to death penalty in the Rajiv Gandhi assassination case, and so death sentence is against Article 22 of the constitution," Justice Thomas, who headed the three-judge bench, told PTI.
"It will be constitutionally incorrect to hang them very late," he said.
In 2010, the Supreme Court bench headed by Justice SB Sinha in the Bariyar case had observed that while passing the death sentence, the personal character of the criminal should be taken into consideration, Justice Thomas said.
Moreover, the three death row convicts in the Rajiv Gandhi assassination case -- Murugan, Santhan and Perarivalan -- have been in prison for over two decades, the former Supreme Court judge added.
For any life imprisonment, every prisoner is entitled to have a right to get his case reviewed, whether remission can be announced or not, he said.
Since the three were death row convicts, they underwent a long period of imprisonment without getting the chance to have a "review" of their case, Judge Thomas said.
Rajiv Gandhi was assassinated by a woman suicide bomber on May 21, 1991, at Sriperumbudur.
A designated court had in 1998 imposed death penalty on 26 persons but when the case reached the Supreme Court, capital punishment was confirmed only for four -- Nalini, Murugan, Santhan and Perarivalan.
Nalini's death penalty was commuted to life imprisonment by the Tamil Nadu Governor in 2000 following a recommendation by the state cabinet and a public appeal by Congress President Sonia Gandhi.
The execution of the remaining three convicts, which was scheduled for September 9, 2011, was stayed by Madras High Court for six weeks in August of that year. The case has since been transferred to the Supreme Court.
Prior to this, the mercy petitions of the three were rejected in 2011 by Pratibha Patil when she was the President, which was challenged by them.