Dad didn't seek Exit advice: Nitschke

Euthanasia campaigner Philip Nitschke now believes the father of a Sydney family of found dead in their home did not contact his organisation, Exit International.

The bodies of Fernando Manrique, 44, Maria Lutz, 43, and their autistic children, 11-year-old Elisa and 10-year-old Martin, were found in their home in Davidson on Monday.

Dr Nitschke says a man by the name of Manrique from Sydney had contacted him about purchasing his euthanasia book.

"(It was) a person of that surname but it was a different Christian name (that) made contact trying to acquire the book," Dr Nitschke told 2GB Radio on Thursday.

Dr Nitschke had earlier told The Australian the dead Sydney father had a digital version of his book.

"When I was first contacted I was away from the database and I said 'yes we had had contact with a person of that name'," Dr Nitschke said.

"The information we have suggests strongly that this was a different person of the same names."

While he conceded the deaths of the children was a concern, no one should judge unless they'd walked in someone else's shoes.

"If people for whatever reason make a decision they want to end their lives, that's a decision they make themselves," he said.

"It's a tragedy no matter how you look at it."

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.

Suicide Call Back Service 1300 659 467.