Angry after a fight about a burnt omelette, Peter John Smith loaded his shotgun and headed for his wife's bedroom.

The 70-year-old told his wife Kathleen he was "going to kill the c--- and then kill myself".

Peter John Smith, 69, murdered his son Andrew at the family home in Mulgrave last year. Credit:Channel Seven

"Of course you are," she replied, not believing her husband of 30 years would follow through with the horrifying threat against their son Andrew.

In sentencing Smith for murder in the Supreme Court on Wednesday, Justice Andrew Tinney said there was no indication the mundane events of December 18 last year would lead to such a shocking incident.