The father of the man who killed six people and injured 12 others in a stabbing at Bondi Junction in Sydney says his son was a tormented soul. 

Eight people remain in hospital after 40-year-old Queensland man Joel Cauchi went on a rampage through the mall on Saturday. 

Australia correspondent Donna Demaio told Mike Hosking that his father, Andrew Cauchi, said he did everything to help his son who was mentally ill. 

Meanwhile, four people are understood to have been injured in a second stabbing attack in Sydney. 

It's understood a teenager entered the Christ the Good Shepard church in Sydney's West before stabbing a bishop in front of his parish. 

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