GAZA, Sept 17 (Nidal al-Mughrabi/Reuters) - A Gaza military court convicted four Palestinians on Monday for kidnapping and murdering an Italian man in 2011, a case that shocked Palestinian sympathizers around the world.

Vittorio Arrigoni, a pro-Palestinian activist, was abducted by a Jihadist Salafi faction, which shares the radical ideology of al Qaeda and is a rival of the Hamas Islamist movement that controls the Gaza Strip.

The group had hoped to force Hamas to release a Salafist leader, Hisham al-Saidni. Hamas police said the kidnappers killed Arrigoni before a deadline they had set for Saidni's release had expired.

Arrigoni's killing horrified international pro-Palestinian activists and tested Hamas's authority in the enclave, which it seized from Palestinian President Mahmoud Abbas's allies in a brief civil war in 2007.

Saidni was recently freed without charge after pledging not to disturb public order, Hamas said.

There was no immediate reaction from Jihadist Salafi groups that have accused Hamas security forces of arresting nearly 40 of their men, some for firing rockets against Israel.

Three of the defendants were identified by the Hamas-run court as Hamas security men who had been working for the Salafi group for ideological reasons. Two received life sentences and one was jailed for 10 years. The men flashed defiant smiles as the sentences were handed down.

The fourth man, a fisherman, fled Gaza after the killing and was sentenced in absentia to 12 months. Two other men were killed in a gun battle with Hamas forces trying to rescue Arrigoni.

They will find justice with God and not with this court, a relative of the one of the defendants muttered.

Lawyers said Arrigoni's family had written to the court to oppose imposing the death penalty. (Editing by Robin Pomeroy)