Supplied video obtained Friday, June 15, 2018 of NSW Police arresting a woman following an investigation into a fatal house fire on San Remo Avenue, Gymea. The woman was taken to Newtown Police Station and charged with murder. (AAP VIDEO/Supplied/NSW Police)

A woman accused of killing her boyfriend by setting fire to his granny flat after turning off the taps has died before her trial for his murder.

Amanda Zukowski, 48, was due to be tried for the 2017 murder of Jeffrey Lindsell, with whom she had an “on-again off-again” relationship.

Mr Lindsell, 39, died from his burns two days after fire ripped through the granny flat he occupied behind his parents’ house in the southern Sydney suburb of Gymea.

Detectives alleged Ms Zukowski tampered with the water supply and deliberately set fire to his home on October 7, 2017.

His parents witnessed their son engulfed in flames and screaming for help run from the burning granny flat at around 1.30am.

Following an investigation by the NSW State Crime Command’s arson unit, in mid-2018 police charged Ms Zukowski with Mr Lindsell’s murder.

Detectives alleged she deliberately lit the fire in the granny flat knowing Mr Lindsell was asleep inside.

At a brief appearance by Ms Zukowski in February last year, Central Local Court heard the accused might be about to enter a plea.

Ms Zukowski, who lit up a cigarette as she walked away from the court where Mr Lindsell’s tearful family was gathered, later pleaded not guilty to murder.

She was on bail and her murder trial was set down for February 3 but has now been vacated due to Ms Zukowski’s death.

candace.sutton@news.com.au