Derek Jackson, 52, who was found dead in his Biddeston home, had a history of criminal behaviour and mental health issues . A grandfather whose body was found alongside his slain seven-year-old grandson and heavily pregnant daughter in a suspected murder-suicide, was well known to police and had a long history of mental illness. Derek John Sharpley, 52, was found dead of gunshot wounds to the head in the same room that his grandson Jackson's body was found tucked into a bed at his Biddeston property, west of Brisbane in Queensland. His 27-year-old daughter Kris-Deann Sharpley, who had moved to the Queensland town in 2011 to care for him following her mother's death, also died of gunshot wounds to the head and was found in the bathroom. Detective Inspector David Isherwood would not confirm the details of Mr Sharpley's criminal history, but told Daily Mail Australia that there had been no recent incidents. 'They [the family] are known to police and in regard to criminal history; the reality is that while he has a criminal history, it's not recent history,' Inspector Isherwood said. 'But he has got a criminal history and there is no doubt that he has had mental health issues.' Mr Sharpley is believed to have attempted suicide in the past and had a history of substance abuse, according to The Courier Mail. Police have stopped short of dubbing the incident a murder-suicide, but have said it is unlikely another party was involved. His daughter Kris-Deann Sharpley (left), who had moved to the town to care for him following her mother's death, was found dead in the bathroom while her seven-year-old son (rigth) Jackson's body was found in a bed . 'I must stress that we are in the early stages of our investigation however it would appear that two of the deaths are suspicious and the death of the man is non suspicious,' Inspector Isherwood said. Mr Sharpley is believed to have shot himself after killing his daughter and grandson, however detectives have been unable to determine the young boy's cause of death after preliminary pathology results returned inconclusive. Inspector Isherwood said there were no signs of physical injury on the child's body and that police were awaiting further results before making any conclusions about how he died. 'There are a couple of issues, they [forensic pathologists] think, with the decomposition. You'd think that with strangulation there would be lesion marks on the neck. What often happens in a lot of bodies in that case is that the head is tilted forward and you get bruising in the front of the body,' Inspector Isherwood said. 'Suffocation is very hard to prove, so the issue we've got is we really don't know'. Detective Inspector David Isherwood told Daily Mail Australia that Mr Sharpley 'was not the owner of a registered firearm', but would not release any other information about the gun used to kill the two adults . Detectives have been unable to determine Jackson's (pictured) cause of death after preliminary pathology results returned inconclusive. Suffocation and strangulation are still being investigated . The owner of the high-calibre gun used to kill both adults, which was found lying on a bed, has also been an unclear aspect of the case. Inspector Isherwood told Daily Mail Australia that Mr Sharpley 'was not the owner of a registered firearm', but would not release any other information about the gun. He said detectives would return to the address on Thursday to obtain any more evidence that could be relevant to the case. It comes after revelations that Kris-Deann  was on maternity leave and excitedly awaiting the birth of her little girl who she'd chosen to name Amber Elizabeth Rose after her late mother when she was slain, her sister-in-law Sara Turnball told the Courier Mail. All three bodies were found by Kris-Deann's (left) sister Tara on Monday evening when she came to the house to pick up some belongings . Detectives will return to the address on Thursday to obtain any more evidence that could be relevant to the case . All three bodies were found by Kris-Deann's sister Tara on Monday evening when she came to the house to pick up some belongings and to see their pet dogs. Tara, who is also pregnant, was accompanied by her boyfriend Allan Brown and had to climb through a window to gain access to the house. Mr Brown told the Courier Mail that Tara screamed out: 'They've been murdered, they've been murdered.' The scene at Toowoomba-Cecil Plains Road home was so grisly it distressed first-response police officers, according to Detective Inspector David Isherwood. A dog barks behind a gate at a house in which the bodies of a man, a woman and a young boy were found in Biddeston, west of Toowoomba, Queensland . Police guard a house where the bodies of the relatives were found on Monday night . 'Two of the victims, both the adult male and female, had very serious wounds to their bodies,' he said. 'Both appear to have been shot in the head.' 'At this point in time there's nothing to suggest there was any incident that occurred in terms of a disturbance.' 'Two people that live in the town heard three distinct gunshots.' The gunshots were heard on Sunday night but locals presumed it was someone shotting an animal. Kris-Deann Sharpley was on maternity leave and excitedly awaiting the birth of her little girl . Kris-Deann shared this photo of her son Jackson and a scan of her unborn child Amber on Facebook before she was killed . 'There is no evidence that the house has been broken into when the police arrived they had to force entry into the premises. It would appear that the house was secure. The first person who attended the residence had to climb in to gain entry.' 'Police attended a Biddeston Southbrook Road address around 6.50pm after the bodies of a man, woman and boy were located. The three aged 52, 27 and 7 respectively, were all known to each other,' Queensland Police said. The shooting happened on the corner of Toowoomba-Cecil Plains Road and Biddeston-Southbrook Road at Biddeston - more than 150 kilometres west of Brisbane. 'There are no concerns for public safety,' a police spokesman said. Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14. Forensic officers took photographs after arriving at the scene on Monday night . Forensic officers are seen outside the house where the bodies of a man, a woman and a young boy were found . Local businessman Paul Farmer described the home owner as 'a quiet, friendly guy' Biddeston is a rural town  in the Toowoomba Region, Queensland, and is home to less than 400 people .
Kris-Deann Sharpley and her seven year old son were found dead on Monday . Her father Derek was also found at the Biddeston house, near Brisbane . Detective Inspector David Isherwood said the grandfather had a history of criminal behaviour and mental health issues . The child's cause of death remains unknown as initial pathology results were unclear, but suffocation and strangulation are still being investigated . The owner of the gun used in the homicide also remains unknown . Police say the deaths of the boy and mother are suspicious but the death of the man is not suspicious .