But, Arthur alleged, his housemates said the plan to use tablets was ‘‘taking too much time’’ and Ms Lyons announced ‘‘it was time to make sure Samantha was dead’’.

Arthur said Mr Lyons instructed him to use a hammer, and that after he drank Jack Daniel’s for ‘‘Dutch courage’’, he went to the bungalow where Ms Kelly was staying.

‘‘Samantha had just come out from the toilet. She asked to see her kids and I said no,’’ Arthur said.

‘‘She went back around to the front of the couch and I walked into the bedroom and picked up the hammer. Then I walked out to the lounge room, where I struck Samantha.’’

Arthur said he ‘‘blacked out’’ after he struck Ms Kelly at least twice, and that he went back to the house to report her death to Ms and Mr Lyons.

‘‘I told Christine the job was done, where she turned around to Ronald and said to go and make sure Samantha is dead,’’ he said.

‘‘Ronald got out of his chair, walked out to the unit and came back and said: 'Yes, you’re the mother of four children'.’’

‘‘Christine was happy ... [She said] ’It’s about time'.’’

Arthur said he began crying while Ms Lyons began talking about changing the names of Ms Kelly’s two youngest children.

The next day, the court heard, the three housemates told people Ms Kelly had left in the middle of the night and had said to Ms Lyons the children were hers.

Arthur said Ms Lyons told Ms Kelly’s children ‘‘that their mum didn’t love them any more and that she ran off’’.

Arthur buried Ms Kelly’s body in a dry creek bed and cleaned the bungalow, he said.

The jury heard Ms Lyons couldn’t have children of her own and that Ms Kelly’s three daughters and a son – who were aged between six and 11 months at the time – were staying in the house with the Lyons, Arthur and Mr Lyons’ three sons, while Ms Kelly stayed in the bungalow.

Mr and Ms Lyons share the same surname because she was once married to his cousin.

They have also pleaded not guilty to attempted murder, related to the allegation they tried to kill Ms Kelly by spiking her drinks with crushed tablets and then fed her prescription pills.

Lawyers for the pair say Arthur acted alone in killing Ms Kelly.  The trial continues before Justice Stephen Kaye.