Deden Sudjana, a member of Ahmadiyya, a minority Muslim sect that many conservative Muslims consider heretical, was found guilty by a district court in Banten Province on charges stemming from the attack, which occurred in February. Judges said he had refused police orders to leave the scene and had wounded one of the attackers.
The judges rejected a charge of incitement leveled by prosecutors, who had sought a sentence of nine months.
The clash, in the remote district of Cikeusik, caused international outrage after a graphic video of it surfaced online. It showed the police offering little resistance as more than 1,000 villagers descended on a home where 21 Ahmadis were staying, killing three of them and then beating and stomping on their mud-covered bodies.
The attack and the trial that followed were widely denounced as evidence of declining religious tolerance in Indonesia, where the police, government officials and the justice system have often appeared reluctant to punish — and, in some cases, are accused of having colluded with — Islamic hard-liners, who have engaged in increasingly frequent attacks on Christian churches and on properties owned by Ahmadiyya.
Last month the same court sentenced 12 villagers, including a 17-year-old who was seen in the video bashing a man’s skull with a rock, to three to six months in jail for their involvement in the attack. Prosecutors did not seek charges of murder or manslaughter.
In the court session on Monday, judges found that Mr. Sudjana, whose right hand was nearly severed in the attack, shared responsibility for the clash because he had helped to stockpile weapons in the Ahmadis’ home, and had resisted police calls to abandon the village, where clerics and villagers had consistently called for the Ahmadis’ departure.
“This sets a very dangerous precedent,” said Firdaus Mubarik, a spokesman for Ahmadiyya. “This decision delegitimizes the right of Ahmadis to defend themselves. It means that they can be punished if they defend themselves when their homes and mosques are attacked.”
Mr. Mubarik said light punishment in cases of sectarian violence only encouraged more attacks on Ahmadis, who are seen by many orthodox Muslims as violating the central tenet that Muhammad is the final prophet.
In the latest such episode, over the weekend, a mob reportedly led by an Islamist vigilante group, the Islamic Defenders Front, damaged Ahmadiyya buildings and assaulted people in the city of Makassar.
Human Rights Watch called on the Indonesian government to set up an independent inquiry into the trial, which “is appalling and smacks of injustice,” Elaine Pearson, the group’s deputy director for Asia, said in a statement on Monday.
Prosecutors in Serang, where the trial took place, rejected the accusation that they had sided with hard-liners. “Deden came specifically from Jakarta to prepare weapons, stones and spears. He was reminded by the police to stay away so there wouldn’t be a clash,” said Hamad Yunus, a member of the prosecution team.
“The citizens who came only wanted a dialogue, but there was resistance from the Ahmadis which started the clash,” Mr. Yunus said.
The defense did not say whether it would appeal the verdict.