The family killed in an apparent murder-suicide in Sydney's north are suspected to have been gassed.
The bodies of Fernando Manrique, 44, Maria Lutz, 43, and their special-needs children, 11-year-old Elisa and 10-year-old Martin, were found in their Davidson home yesterday.
The family showed no signs of physical injury and their dog was also found dead.
"Police are looking at the possibility the family members died from the introduction of an airborne gas," New South Wales Police said in a statement.
The children's specialist school, St Lucy's, raised the alarm when Ms Lutz didn't turn up for canteen duty yesterday.
Ms Lutz's sister, Ana, called her sibling a "warrior".
"My beautiful doll ... one more angel in heaven. An angel dedicated to your children, life! I love you fighting untiringly for others. Always in my life, in my heart. I love you" she wrote on Facebook.
Ms Lutz was reportedly found in a room with one child, while Mr Manrique and the second child were found in different rooms.
Acting St Lucy's principal Warren Hopley said staff and students were devastated and described Ms Lutz as "an exceptional woman".
A prayer service for the family was held at the school today.
"They were wonderful, a fantastic family. They had time for everyone, devoted so much time to the school," Josie Gigliotti, a parent of one of Elisa's classmates, told AAP.
"But, you know, we're all there for each other. She was so strong, she never really let us in to know how hard she was doing it.
"Pray for us, our school and our community. Because we are going to be struggling with this."
Readers seeking support and information about suicide prevention can contact:
Lifeline (open 24/7) - 0800 543 354
Samaritans (open 24/7) - 0800 726 666
Suicide Crisis Helpline (open 24/7) - 0508 828 865 (0508 TAUTOKO).
Youthline (open 24/7) - 0800 376 633. Email email@example.com.