The statements were handed to police on the island by the Sydney lawyer who obtained them before he was deported from Manus Island on Friday, after being shut out of the detention centre in defiance of a court order.

Police revealed two Australian employees of security contractors G4S were wanted for questioning over the violence, which came after asylum seekers say security guards and others broke into the centre.

''They are expatriates … but they returned to Australia soon after the incident. We are recommending that once we have completed our investigation of these two people, we will ask that they be extradited back to PNG to face possible criminal charges,'' a police source said.

The statements are from three asylum seekers who say they saw how Mr Barati died, including his room mate; one who was attacked, then shot in the buttocks when he fled and was bashed again; and one whose throat was slashed while he says two men pinned his arms.

Fairfax understands one of the witnesses says PNG guards, PNG locals and expatriate Australians were involved in the death and he can identify most of them by face or name.

The police source said PNG investigators knew the first names of the two men wanted for questioning. Fairfax Media has chosen not to publish them.

The source, citing a police report from March 26, compiled by Chief Superintendent Anthon Billie, acting divisional commander for the islands region of PNG, said that ''a major obstacle'' to the investigation had been G4S and its employees' refusal to co-operate with the PNG police investigators.

The firm and its workers have insisted on speaking instead to the Australian Federal Police, the source said, adding that PNG had requested that two AFP officers be sent to Manus Island to help with the investigation.

The AFP had not responded by deadline to Fairfax Media's questions.

No reason was given for the deportation of the barrister, Jay Williams.

The deportation ignored an order from the PNG judge investigating human rights at the centre who gave Mr Williams access to the centre before a new inquiry was due to open on Monday. The lawyer had been granted access to the centre between 10am and 4pm each day this week by Justice David Cannings, who instituted a constitutional inquiry into human rights at the centre after the violence.

When the PNG government, acting after consultations with Australia, moved to shut down his inquiry on the grounds that he was not impartial, he set up a second inquiry and gave orders giving Mr Williams access.

Fairfax Media spent four days on Manus this week and spoke to many locals who supported the economic spin-offs from the detention centre, but argued that the asylum seekers should have more human rights.

A spokesman for G4S strongly denied the company had failed to co-operate with PNG investigators. He said police had interviewed 10 expatriate G4S officers.