The person believed to have shot dead three people on a property in rural Queensland is custody as details of a potential motive for the killings slowly come to light.

The alleged gunman is one of three people currently being held by police, while a fourth victim continues to recover in hospital after being shot in the stomach.

The victims are all from the same family and have been named in multiple media reports as Mervyn and Maree Schwarz, and Maree's son Graham Tighe.