THE DISCOVERY of a body, concreted into a 44-gallon barrel, during a family adventure along the banks of the Caboolture River began the unravelling of a missing person mystery that led police to the "best mate".
Burpengary dad Simon Hay called police as he quickly ushered his two children away from the barrel.
Norman Desmond Cheney's jaw, skull and teeth were visible at one end of the barrel, his foot at the other.
Anthony Charles Oliver, 39, admits he is responsible for loading the body into the barrel, allegedly with the help of his brother-in-law Peter Harris at the Esk property where he lived with sister Jenny Oliver, and dumping it in the river.
But he pleaded not guilty in Brisbane Supreme Court on Monday to murder.
Mr Oliver, who was in a love triangle with his mate and his wife Trichelle Cheney, says he killed Cheney out of self-defence.
Mr Cheney had a gunshot wound to the head and a slit throat.
Defence barrister Michael Byrne said Mr Cheney, 41, had a history of becoming "incredibly violent in a very short time frame" and his outbursts were exacerbated by his frequent use of the drug ice.
He said Mr Cheney was bipolar and witnesses would testify about his mood swings and paint a picture of jealousy, possessiveness, obsession and violence towards former partners.
Mr Byrne detailed an incident where Mrs Cheney's former husband walked in to find her in bed with Mr Cheney.
He said while the former husband should have the right to feel wronged by the affair, Mr Cheney "flogged" him to the point he was hospitalised and had steel plates inserted in his head.
The court heard Mr Cheney was last heard from on December 20, 2010, and his body was discovered on February 5, 2011, at Rocksberg after extensive flooding in the Caboolture area.
Crown prosecutor Todd Fuller said Mrs Cheney had been having an affair with Mr Oliver, though there was a brief interval while she worked on her marriage with Mr Cheney.
He said Mr Cheney, apparently oblivious to the affair at the time, moved in with Mr Oliver after the separation in December, 2010.
Mr Fuller said a car used to transport Mr Cheney's body was found burnt out at Crows Nest and blood was found in a shed at the Esk property.
He said a .45 calibre handgun was found stuffed in a Snoopy toy at the house of Mr Oliver's wheelchair-bound friend at Caboolture.
Pathologist Nathan Milne said the most significant post-mortem find was the gunshot wound to the head, which would have caused instantaneous death.
He said if the slice to the neck had come first, it would have hit the carotid artery and blood loss would have caused death within 5-10 minutes.
But Mr Milne said he could not rule out that the edge of the barrel caused the sharp cut after death.
He said he could not exclude that methylamphetamines in Cheney's system, which were in the potentially fatal range, caused the death but they could have been artificially elevated because of body composition changes after death.
Mr Milne said the illicit drugs - which were combined with anti-psychotic and other mental health related drugs - could have contributed because the toxicity could have impaired behaviour or reduced consciousness.
The trial continues.