The commander of an Australian platoon that lost three soldiers in Afghanistan to an insider attack insists he did everything he could to protect his men.

An Australian army captain whose platoon lost three soldiers in Afghanistan failed to protect his men by leading a mission into a Taliban stronghold without proper precautions, an inquest has heard.

Captain Dominic Lopez was in charge of a 24-man mentoring task force to a patrol base in Oruzgan province, Afghanistan, when three soldiers were gunned down by an Afghan National Army sergeant in 2012.

Capt Lopez was reduced to tears at an inquest on Thursday into the deaths of Lance Corporal Stjepan Milosevic, Sapper James Martin and Private Robert Poate, following accusations he failed to take proper security precautions on the mission.

The Brisbane inquest has heard Afghan soldiers were allowed to mingle with Australians at the Wahab patrol base and only one Australian guard was on duty when the gunman, named Hekmatullah, opened fire with a machine gun on the night of August 29, 2012.

Capt Lopez said he was unaware that at the time defence security policy had been tightened following a dramatic increase in the number of so-called green on blue attacks.

He also admitted the only intelligence he had about Wahab before deploying was from aerial photographs.

Barrister Peter Bodor QC, for Pte Poate’s family, accused him of failing to realise the “clear and present danger” of deploying to a remote patrol base in a Taliban stronghold.

“You think you did your job, did you? I put it to you that you were blind, you blinded yourself to the responsibility,” Mr Boder said.

The captain replied: “It was a responsibility that I did not take lightly.”

Mr Bodor returned: “There are three families here grieving because you didn’t do your job.”

Capt Lopez broke down in the witness box before Deputy State Coroner John Lock cautioned Mr Bodor.

The soldier insisted the measures he took to protect his men were adequate and nothing could have stopped the gunman.

“Hekmatullah had multiple avenues open to him to conduct this act. If he was committed – which he was – to conduct this attack it would have occurred,” Capt Lopez said.

The inquest, which was closed to the public for several hours due to classified evidence, also heard that deaths from green on blue attacks in Afghanistan skyrocketed from two in 2008 to 39 in the eight months leading up to the deadly incident.

Capt Lopez admitted vital information wasn’t passed on to him before the 24-man contingent landed at the patrol base, including a policy to ramp up security measures, and that Afghan soldiers weren’t able to be separated from Australians at that particular base.

The court heard that Hekmatullah had strong ties to the Taliban and the mission was “a disaster waiting to happen”, in the words of counsel for Sapper Martin’s family, Alan MacSporran QC.

The inquest continues on Friday.