A forensic pathologist says any one of three shots would have killed Timothy Bourke of Whanganui.
His brother, David John Bourke, is on trial in the High Court in Palmerston North for murdering Mr Bourke in October last year.
He is also charged with causing grievous bodily harm to a farm worker near Norsewood on the same day.
The court heard on Monday that the accused killed his brother to end months of pain and suffering, and three shots had to be fired from a .22 calibre rifle to kill him.
However, Dr John Rutherford, who conducted the post-mortem, said each of the three bullets would have killed him.