At about 9.55pm last night, a man called Triple Zero to report he’d found his father stabbed at an address in Hillview St, Roselands.
Two officers entered the family home and found a 91-year-old man with fatal stab wounds.
The officers suffered chemical burns from what is believed to have been hydrochloric acid, which police said had been spread around the house.
They were taken to hospital but have since been released and will be back on shift this afternoon.
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A 24-year-old man was arrested at a nearby property.
He is under guard in hospital undergoing treatment for injuries which may require surgery, and has not yet spoken to police.
Area commander Superintendent Sheridan Waldau said the man was injured prior to his arrest.
She said the incident appeared to be a family-related matter.