A MAN who murdered a $5m lottery winner after believing her and her husband to be "wasteful'' will spend at least the next 13 years in jail.

Peter Joseph Kelly, who was the accountant for Maria Lou Devrell and her husband, had known the couple for 20 years before he bashed Ms Devrell with a rubber mallet covered with cling wrap on March 28. 2011.

The 54-year-old Central Coast man had the power of attorney for his victim at the time of the killing, later told psychiatrists he "was just so furious'' with her and "saw crimson'' during the argument that foreshadowed the murder.

The Supreme Court heard David Devrell, Maria's husband, asked Kelly to manage their finances once they won a $5 million lotto prize in 1999.

But Kelly became frustrated with Ms Devrell's spending habits, the court was told.

"A situation emerged in which they were spending money more quickly than it was being allocated to them by the offender,'' Justice Robert Allan Hulme said in sentencing Kelly to a maximum of 18 years in jail.

"He seems to have had the attitude that they were being wasteful.''

The Crown said Kelly had murdered her because his investment decisions had put half of their winnings at risk, but his defence barrister told the court last month that he had "hit back'' at Ms Devrell after she had attacked him first.

Ms Devrell was struck on the back of the head with the mallet, and then hit another few times when she screamed for help, the court heard.

He then covered her mouth with his hand to silence her, and it was that asphyxiation which caused her death.

Ms Devrell's body was discovered in a pool of blood by her daughter several hours later.

Justice Hulme rejected Kelly's claim he hadn't intended to kill her and only wanted her to "lose all memory'' of the argument they had.

"I thought that when she awoke it would be like starting afresh and that we could discuss the matter rationally,'' Kelly told police.

"After he had struck her head, he did not wait around for her to wake up,'' Justice Hulme said.

"After the argument had ended with [Kelly] pushing [her] to the floor, he walked outside to his car and, it would seem, stewed over whether and how to vent his anger further.

" He then chose his weapon and took the care to wrap it in cling wrap in an attempt to avoid evidence that would incriminate him being in his possession after the event.

"This tends to indicate a degree of cold and calculating deliberation.''

The court heard Kelly would have been sentenced to 24 years in jail were it not for his guilty plea last year, when he also admitted to taking her purse to make the crime look liked a botched robbery.

Justice Hulme said Kelly had led "an otherwise blameless life'' and had good prospects of rehabilitation.

He will be eligible for parole in October 2024.

Originally published as Lotto winner killed over 'wasteful' habits