G4S has told a Senate inquiry that the Department ignored its warnings and sent the dog squad in to control the escalating situation in the centre.

Twenty-three year old Iranian asylum seeker Reza Berati died during the violence in February this year.

The security contractor says ordering local police to enter the compound marked a violent turning point.

"If there is a mob mentality that night, it was when that occurred," Chris Manning, G4S Australia's Managing Director of Immigration told senators.

He says G4S was against sending local PNG mobile police into the compound.

"We were overruled [by the Department]", Mr Manning says.

Managing director of the Manus Island detention centre agrees.

"I had some concerns, as we all did, that if we called in the police, what would happen," Kevin Pye says.

The Guardian Newspaper reported on the fact that the police dog squad was invited into the centre shortly after the incident occurred.

The Immigration Minister would not be drawn on the issue at the time, citing the eminent release of the Cornell Review into the incident.

Head of the Department of Immigration distanced himself from the decisions made on the island, saying it was ultimately the responsibility of security contractors and PNG authorities.

But Secretary Martin Bowles admitted in the Senate Inquiry that the Department did not have a comprehensive list of all subcontractors working in its centre. Nor did they ask for one from G4S.

"We do not... tell them how to run their business," Mr Bowles says.