A heartbreaking note has been found at the home where three children and their mother were found dead.
It's believed that the mother carried out the killings before taking her own life.
Keep scrolling to learn more.
Last week tragedy struck.
When three children and their mother were found dead at their home.
The incident took place in Tullamarine, Australia.
And police believe the children were killed by their mother in Tullamarine before she took her own life.
The children were all under the age of seven.
The children were aged seven, five, and three.
The children's father, Tomislav Perinovic, was initially questioned by police.
But he was released without charge and officers do not believe he or anyone else was involved in the awful tragedy.
They believe his wife, Katie Perinovic, 42, was responsible for the deaths of her children.
And neighbours of the pair have been left both heartbroken and completely shocked upon learning of the horrific murders.
Friends and neighbours laid bouquets of flowers for the victims and their surviving relatives on Friday morning.
And none of them really understand what happened - saying that the children and parents always seemed so happy.
Marie Groves, a neighbour and family friend of the late mother, said:
"Those kids were full of life. They were your picture perfect kids,' she said. 'She loved those kids so much and would do anything for them."
She attended a party with the mother in November.
And claimed that she was quieter than ever before - but of course, she was not expecting anything like this.
More specifically, Ms Groves, said:
#BREAKING: Homicide Squad investigators believe Katie Perinovic was “responsible” for her own death, as well as the deaths of her three children - Claire, 7, Anna, 5, and Matthew, 3.— Monique Hore (@moniquehore) January 15, 2021
Her husband, Tomislav, has been released without charge.
FULL @VictoriaPolice STATEMENT: pic.twitter.com/tvrf0LRhoW
"She was more withdrawn than I've seen her ever in the past,.
"There were a few other mums here and they did notice she seemed a bit quiet on that day. But she never mentioned anything like that."
The family's neighbours, Kevin and Clare Harrison, cried when they heard the news.
Devastated friends and family are searching for answers after Katie Perinovic killed her three children, then herself, inside their home.— The Advertiser (@theTiser) January 16, 2021
* PLEASE RESPECT THE FAMILY'S GRIEF IF COMMENTING ON THIS STORY *
👉 Lifeline: 13 11 14 or https://t.co/g6P99Pjk2nhttps://t.co/uWMOiojoZF
"We shared coffees, we have sat on their front veranda and just laughed at the kids and the way they just ran around in the yard.
"I used to talk to Tom while he was teaching Matthew how to ride a bike everyone around here was involved with them because of the kids."
#Breaking - Homicide squad detectives have released Tullamarine dad Tomislav Perinovic without charge. Victoria Police have formed the preliminary view Katie Perinovic is responsible for all four deaths. A report will be prepared for the coroner. Lifeline: 13 11 14. @theheraldsun— Brianna Travers (@briannatravers) January 15, 2021
"Christmas Day, every year we have given the kids Christmas presents because we have known them from birth."
They described them as the 'friendliest, loveliest people'.
Rest in peace Katie Blazevic (Perinovic) with your beautiful children. It has been over 20 years we last spoke and saw each other, but your beautiful laugh and easy going nature will forever be in my memories. Even then you were so passionate about physiotherapy. Heartbroken...— Zerina Tomkins (@TomkinsZerina) January 15, 2021
And added that they may never be able to fully get over the horrific news.
In fact, all of their neighbours said the same thing.
Tullamarine mum Katie Perinovic, nee Blazevic, & her 3 young children found dead in what has been described as a “gruesome” scene. Her husband Tom, who called triple-0 is assisting police. @theheraldsun https://t.co/4qOkChQ2zY pic.twitter.com/X74aWNGvos— Brianna Travers (@briannatravers) January 14, 2021
Phil Funaro, who has lived on the street for over 30 years, explained how he used to see the family on the way to the park.
It's understood Melbourne mother Katie Perinovic - who was found dead alongside her three children - killed her children before taking her own life in what police are treating as a murder-suicide. pic.twitter.com/iramWHMgGo— Andrew Backhouse (@Andytwit123) January 15, 2021
"I mainly saw Kate and the three kids, couple of times saw the husband with them, always like mother hen with the three young kids at the back.
"She was very friendly, always there with a smile on her face."
He said there were no signs anything was wrong in the house.
48-year-old Tomislav Perinovic has been released without charge following the deaths of his 42-year-old wife Katie and three children Claire, Anna and Matthew. Police believe the 42yo woman was responsible for all four deaths @abcmelbourne— Bridget Rollason (@bridgerollo) January 15, 2021
Before saying: "You would not pick it. You would not pick it."
Now in the days following the gruesome murders.
There are still some reminders of the happy normality that once existed within the family home.
There was a drawing of the Earth.
The drawing of the Earth, which was done by oldest daughter Claire, was stuck in the main window. 'Save the world,' it said, alongside a love heart.
Another heartbreaking note was found written by one of Claire's friends.
The note simply reads:
"Claire was my BFF always."
Such a tragedy.
At the time of writing, police continue to investigate the grisly murder.
Rest in peace.
Our thoughts go out to the family's friends and close ones during this incredibly difficult time.