Amnesty International says expert analysis shows bullets were fired directly into the Manus Island detention centre during the Good Friday riot, and that the Australian government intentionally downplayed the risk to refugees and staff.

In a report released on Monday, the human rights group says digital and military experts have verified images and footage from the Good Friday shooting, and their findings contradict claims made by Australian immigration officials that only one weapon was discharged, and that only into the air.

In a statement issued to the Guardian after the Good Friday event, the Australian Department of Immigration and Border Protection said, “PNG military personnel discharged a weapon into the air during the incident.”

However, staff, refugees, and asylum seekers in the centre reported hearing 100 shots fired into the detention centre, piercing fences and hitting buildings where they were sheltering.

The Amnesty report says video footage shot during the riot and images taken in its aftermath, showing the damage caused by bullets, demonstrate that several bullets were fired into the detention centre where staff and refugees were hiding.

“Our investigation shows there is no doubt that on 14 April 2017 bullets were fired not only into the air but directly into the Manus Island refugee centre in a way that seriously endangered the lives of the people inside,” Amnesty International’s Pacific researcher, Kate Schuetze said.

“This was not an isolated incident. Refugees trapped on Manus Island have faced several violent attacks in the past. They are the direct result of an inherently abusive system put in place by the Australian government.”

Detainees say more than 100 shots were fired and many hit buildings and fences in the detention centre. This photo was received the following day with the damage marked on it

The PNG government says its investigation into the Good Friday shooting is continuing. No arrests have been made.

A spokesman for the Department of Immigration and Border Protection told the Guardian: “this is a matter for Papua New Guinean authorities. The Royal Papua New Guinea constabulary and the PNG defence force are conducting concurrent investigations into this incident. As such, it would be inappropriate to comment further.”

Schuetze said the Australian government had failed to take responsibility for people’s lives, arguing the immigration minister, Peter Dutton, sought to diminish the seriousness of the shooting.

“Instead of waiting for the results of an investigation, Dutton has inflamed matters by making an irresponsible and unfounded claim about the shooting incident.”

The riot on Good Friday, the second time armed assailants have attacked the detention centre, was sparked after a dispute over the use of a soccer field nearby to the detention centre.

“Drunken soldiers … went on a rampage” according to PNG police. The defence force personnel attempted to storm the centre, firing weapons at refugees and staff hiding inside, and even using a vehicle to try to ram the gates.

Dutton said the riot was sparked over concerns that a Manusian boy had been able to enter the centre where he was given fruit.

“I think there was concern about why the boy was being led, or for what purpose he was being led, away back into the regional processing centre.”

However, it later emerged that the boy went into the centre – having asked for food – a week before the riot, and the minister’s account has been contradicted by PNG’s police and defence forces, members of parliament, staff in the centre, as well as the refugees and asylum seekers who were there.

Manus police chief David Yapu refuted Dutton’s claim the incident with the boy was being investigated by police: “There is no complaint being made by the parents of the boy.”

The three refugees who assisted and fed the local boy, who came to the centre gates asking for food, have pleaded with authorities to release CCTV footage of the boy going into the centre which they say will vindicate their version of events.

“We helped a hungry and poor child who was requesting for food or money. He was fluent in English and begging for food,” the said in a formal complaint to detention centre managers Broadspectrum.

“All of these incidents is recorded by your CCTV cameras. We are requesting for the immediate release of the footage of this incident. We didn’t do any wrong except helping a poor boy.”

Refugees inside the detention centre have said the Good Friday shooting was reminiscent of the February 2014 riots when police and guards stormed the centre, breaking down fences and shooting at refugees. More than 70 refugees were seriously injured in three days of violence, including one man shot, and another who had his throat slit.

Reza Barati was murdered by guards who kicked the Iranian asylum seeker as he lay on the ground before dropping a rock on his head.

After releasing its latest report, Amnesty has renewed its calls for the detention centre on Manus Island to be shut down.

“Until that system is dismantled and the refugees are brought to safety, the threat to their lives will remain,” Schuetze said.

More than 800 men are still held in the Manus Island detention centre, about 100 are living in a transit centre nearby to Manus’s main town, Lorengau, or elsewhere in PNG.

Of the men remaining in the detention centre, about 700 have been formally recognised as refugees and are legally owed protection. About 160 men have had their claims for protection rejected.

Officials from the US departments of state and homeland security have been on the island conducting preliminary interviews about resettlement in America, however no one has yet been accepted.

Extra police have been deployed to the Manus centre, to help Australian and PNG authorities force refugees to relocate to the transit centre.

The Australian Border Force deputy commissioner Mandy Newton told PNG’s national broadcasting corporation police would help prevent unrest during the relocation.

“Because we don’t want any trouble to occur, we don’t want any rioting to occur. We want to consult with the people in the centre – which we have been doing now for some years – but it’s important also that people know they can’t behave inappropriately, either in the community or within the centre.”