Jacqueline Bartlam could be identified only by dental records, after her body was recovered from the blaze on April 25 last year.
The court heard how her son, Daniel Bartlam, had been inspired to carry out the killing by a plot in Coronation Street, where one of the characters John Stape, had killed a woman with a hammer.
Bartlam had claimed the killing was not murder because he had lost self-control.
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The slump will spark scrutiny, especially as statistics show a rise in racially or religiously motivated offences following the EU vote.
The 53-year-old was killed shortly after leaving her home in Mosta, Prime Minister Joseph Muscat said.
Jordi Sanchez of the Catalan National Assembly and Jordi Cuixart of the Omnium Cultural group were jailed on Monday.