Dora, wife of fisherman Gelastine, said: “This is a conspiracy at the highest level. The Indian government should ... bring back the two marines to stand trial in our country.”
The other fisherman who died is Ajesh Binki.
A furious Kerala Chief Minister Oommen Chandy termed the Italian move unacceptable.
The Left Democratic Front in Kerala accused the Congress-led state and central governments of “colluding” with Italy.
“This has taken place because all the players in this ... colluded for this to take place,” Marxist leader Kodiyeri Balakrishnan, a former Kerala home minister, told IANS.
The Bharatiya Janata Party (BJP) was equally critical.
“It was a planned strategy and looks like a diplomatic collusion between India and Italy,” party spokesman Balbir Punj said.
“People who murdered two Indians are getting away scot free. We want to know under whose influence this is happening.”
Another BJP leader, Rajiv Pratap Rudy, said it was “bluff and betrayal” by the Italian government and India should respond strongly.
“A big question arises over the role of the Indian government.”
When the Italians were allowed by the Supreme Court to return to Italy for a second time (they went during Christmas and returned), Rome's ambassador here had promised that the two would positively return to India.