Aussie who killed lotto winner for 'being wasteful' to spend at least 13 years in prison

Peter Joseph Kelly, 55, pleaded guilty to murdering Maria "Lou" Devrell in her Tamworth home on March 28 last year by hitting her over the head with a mallet wrapped in cling film and suffocating her.

Justice Robert Allan Hulme handed down a maximum sentence of 18 years in the NSW Supreme Court on Friday for the killing, which he said was carried out with "cold and calculating deliberation".

The court heard Kelly had been a friend of Ms Devrell's husband, David Devrell, for 25 years, and took over the management of the couple's finances after they won the lottery in 1999.

But Kelly became increasingly angry with the couple, who he believed were "wasteful" with their $5 million winnings, Justice Hulme said.

On the day of the murder, Kelly was due to go camping with Mr Devrell but he called in first at Ms Devrell's home.

The pair got into an argument over Ms Devrell's desire to be allocated more money, and Kelly told police he became furious and was "seeing crimson".

He went out to his car and returned with the mallet wrapped in cling film, which he used to hit Ms Devrell over the head several times.

He suffocated her and took her purse when he left, to make the crime look like a robbery.

Handing down the sentence, Justice Hulme said, "I have been left with the distinct impression that the full truth behind the killing of Mrs Devrell has not been told."