Inside the sordid household love triangle that shocked Australia – as family reveal WHY mum sat within the entrance seat whereas her son had intercourse together with his sister-in-law

A mother sat in the front seat of a car while her son and his sister-in-law had sex in the back because she was the only one with a licence to drive them to their secret rendezvous at a housing commission parking lot, relatives have revealed.

Great-grandmother Sue McCulloch was living with her son David McCulloch and his wife, Jacinta King, and their four adult children at a home in Ulverstone, northern Tasmania, before their lives were turned upside-down on March 28.

That evening, Sue hopped in the car and drove to the home of her younger son, Jamie McCulloch with Jacinta as her passenger. She then drove them both about 26km to a government-owned block of flats in Devonport, where her grandson had been living.

David and Jacinta’s son had given his grandmother the keys because he was away and thought she might want to stay there for a break from the family home. 

‘Mum saw that as an opportunity,’ he told Daily Mail Australia. 

He then explained that Jacinta had ordered his grandmother to drive to the unit and to stay in the car while she had sex with Jamie, and Sue reluctantly complied.

The situation turned to disaster when David realised what was going on and drove to the unit block, tore through the parking lot and smashed into their car, before going on a rampage with a shovel. 

As David now does time in jail for assault, Jacinta and Jamie have shacked up together in a squalid caravan parked in the driveway outside a suburban home.

When approached for comment on Wednesday, Jamie described the situation as ‘hog wash’, but was otherwise unable to string a coherent sentence together.

Asked if he knew if his brother was in jail, Jamie laughed and mumbled: ‘I know.’ 

On Thursday, the new couple drove together to the Salvation Army store in Devonport and appeared disappointed when it was closed. 

The violent altercation on March 28 only ended when a concerned resident phoned police.

The resident told Daily Mail Australia that she saw Sue’s car out the front that night, but didn’t realise what was going on until David grabbed the shovel and started banging on the vehicle.

She recalled him screaming: ‘You’re nothing but a dog, you f***ing dog, you’re meant to be my brother, how could you root my wife?’

Sue locked the car doors and Jamie continued to have sex with Jacinta, until David prized it open and started throwing punches.

David then turned to Sue, screaming, ‘You’re no mother, f***ing a**hole, you’re nothing but a sl*t,’ and shoved her into a wheelie bin.

Jamie tried to run away and hide in some nearby bushes, but David found him and started laying into him with the shovel, the resident recalled.

‘And not the flat end [of the shovel],’ she added. 

‘The sharp side, right in the neck, side and leg, saying he wanted to kill him, and then he turned to Sue and said he wanted to do the same to her.

‘It looked like he was trying to behead him.’

Police arrived and David was charged with a string of assault-related offences, while his wife and brother were taken to Mersey Community Hospital with bruising and minor lacerations.

During his police interview David expressed extreme frustration over the incident and claimed that his brother ‘deserved it’.

Speaking with Daily Mail Australia, David’s son expressed the same sentiment.

Referring to his parents, he said: ‘A man loved a woman and she didn’t love him back, end of story.’

He said the affair had been going ‘for years’, and his father ‘finally cottoned on and cracked it’.

‘They’re dead to me,’ he said.

‘I want nothing to do with them, my siblings want nothing to do with them.’

Police raided David and Jacinta’s property following the arrest on March 28.

They found an unsecured homemade gun in the laundry and about 240g of cannabis in zip-lock bags. He later confessed to selling and supplying the drug. 

David pleaded guilty to a string of assault charges, along with possession of cannabis and a homemade firearm.

During sentencing in Burnie Supreme Court last week, Justice Tamara Jago accepted the circumstances surrounding the violence were ‘confronting’.

She said: ‘The betrayal by your wife and brother, and the apparent acquiescence of your mother, must have been upsetting, and whilst one can appreciate that would give rise to a level of angst and frustration, it in no way excuses what you then did. 

‘It does, however, place your behaviour into a specific context. 

‘This was not premeditated or planned behaviour, but rather was a spontaneous reaction to you discovering a difficult situation involving a breach of trust.’

The judge said David intended to commit grievous bodily harm on his Jamie, but – given the mild nature of his injuries – it was unlikely the majority of blows with the shovel actually connected with his body. 

She continued: ‘The actual harm occasioned was moderate.’

‘There is no question that what you did was exceptionally serious and your use of the shovel had the potential to cause serious harm, but the context in which the violence was committed was, in all of the circumstances, morally provocative.

‘You reacted most inappropriately, but I accept it was an emotive response to the circumstances that you had discovered.’

She was satisfied that David was not at risk of reoffending and took his early guilty pleas into consideration, but said the sentence had to reflect the serious nature of the crimes and serve as a general deterrence.

He was sentenced to three years’ imprisonment, backdated to May 7 when he was taken into custody.

The final 18 months of his sentence will be suspended on the condition that he does not commit any crimes for two years.

David was also fined $1,000.