Myanmar's military responded to the insurgent raids with reprisals. It then forced some 700,000 Rohingya Muslims out of the mainly Buddhist country where they have faced persecution for years.
The government denies any widespread abuses and has accused rights groups of a pro-Rohingya bias while highlighting the suffering of other ethnic groups swept up in the violence.
Amnesty spoke to dozens of witnesses and survivors of the attacks in Rakhine in August have detailed how Hindu men, women and children were killed by Arsa militants armed with knives, swords and sticks.
The Amnesty report, which has been verified through hundreds of witness accounts, is likely to be controversial because it backs up the assertion by Myanmar's military and government that their campaign of violence carried out in Rakhine last year was in response to Arsa's actions.
The accounts by witnesses also reveal the level of fear that victims had about telling the truth. The report also highlights the story of eight Hindu women who fled to refugee camps in Bangladesh were pressured by Arsa to make videos claiming the Myanmar military carried out the violence against them.
Laura Haigh, an Amnesty researcher who helped compile the report, said it had been "very difficult to get people to open up about Arsa, they are a very elusive group, and there is a fear among the community now in Bangladesh, with the informant killings last year, not to speak out and that there could be reprisals against those who do." (Guardian)
"Accountability for these atrocities is every bit as crucial as it is for the crimes against humanity carried out by Myanmar's security forces in northern Rakhine State," she said,
Hindus were the target
ARSA attacked the Hindu community in the village of Ah Nauk Kha Maung Seik, in a cluster of villages known as Kha Maung Seik in northern Maungdaw Township around 8 am on Aug 25, 2017.
The killings came just days after ARSA fighters unleashed a series of attacks on around 30 Myanmar security posts on Aug 25 in 2017, prompting an unlawful and disproportionate violence by Myanmar's security forces that forced more than 693,000 Rohingya people to flee to Bangladesh, where they still remain.
"The full extent of ARSA's abuses and the Myanmar military's violations will not be known Until independent human rights investigators, including the UN Fact-Finding mission, are given full and unfettered access to Rakhine State," said the director of Amnesty's Crisis Response.
Reaction in India
The violence the ARSA carried out may not go down well in India where tens of thousands of Rohingya live. India is predominantly Hindu and groups have been asking the government to oust the Rohingya and send them back to Myanmar. The global community must make a distinction between refugees and militants. The militants must be tackled with full force and refugees must be given protection until they can stand up on their own feet.