The MPs said the convicts--Santhan, Perarivalan and Murugan--have been in prison for more than two decades.
In a memorandum to the Prime Minister, they also demanded abolition of death penalty.
"The death sentence of the three convicts should be commuted to life sentence on humanitarian grounds, taking into consideration the long period of imprisonment they have already undergone," they said.
The MPs said the government should adopt a resolution in this regard in the Union Cabinet and recommend it to President Pranab Mukherjee.
"On behalf of our leader M Karunanidhi, we request you to consider the cases of Murugan, Santhan and Perarivalan, which will also come under the same line. Their conviction was upheld by the Supreme Court in May 1998. They are suffering imprisonment for more than 22 years ever since their arrest in 1991," the DMK members said in their memorandum to the Prime Minister.
