"We do not cease to work tenaciously to bring them home," Napolitano said after his speech on National Unity and Armed Forces Day.
The case triggered a drawn-out diplomatic row between India and Italy, with Rome contesting India's right to jurisdiction.
Meanwhile, Foreign Minister Emma Bonino was quoted as saying by Italy's ANSA news agency that the case of two Italian marines "is moving" and may be changing for the better.
"I think some things are moving in this sense and we are working on (this)," Bonino said of Italian efforts to have the marines transferred from India back to Italy.
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On February 15, 2012, two Indian fishermen on a fishing boat were shot dead allegedly by members of an Italian Vessel Protection Detachment deployed on MT Enrica Lexie at approximately 20.5 nautical miles off the coast of Kerala.
The two marines -- Massimiliano Latorre and Salvatore Girone -- were arrested after the incident and are being tried for murder.
Bonino has stated that the Italian government's objective is to see the pair return home and today she said the government "speaks with one voice" and should be able to "unravel the tangle" of the complex diplomatic and political situation.
"The work to bring home Massimiliano Latorre and Salvatore Girone is constant, determined, and pressing even when made with discretion and without noise," he said.