"I'll be able to see them again one day": The lone survivor of a horrifying family shooting speaks.

Warning: This post contains graphic details of violence, including violence against children, and may be extremely distressing for some readers.

In a family photo splashed across countless newspapers this week, the Stay family are a picture of pure joy.

There’s Mum (Katie, 34) and dad (Stephen, 39) and the five kids, all sitting on a swing seat dressed in jeans and blue shirts. The kids – Bryan, Emily, Rebecca, Cassidy and Zach- range in age from four to 14. That’s Zach you can see grinning cheekily as he perches on dad’s knee.

But what was once a joyful family photo has now become nothing short of haunting.  No one could have predicted the tragedy that would befall the Stay family last week — or that 15-year-old Cassidy would be the only one left to tell the horrifying tale.

Last Wednesday,  33-year-old Ronald Haskell allegedly barged into the Stay family home in a middle-class suburb outside Houston, Texas.

It is alleged that Haskell, dressed as a FedEx delivery man, broke down the door of the four-bedroom house after Cassidy refused to let him in.

Police say Haskell, the ex-husband of Katie Stay’s sister Melannie,  demanded the children tell him of Melannie’s whereabouts — and when the children did not, the unthinkable happened.

Haskell allegedly tied them up and, when the parents arrived home, lined up the entire family of seven on the ground before shooting them, execution-style, in the back of the head.

The entire family – dad Stephen Stay, mum Katie Stay and their four children  — all died at the scene. Except for Cassidy.

Somehow Cassidy miraculously survived.

In a remarkable show of quick thinking and bravery, the fifteen-year-old played dead after her family were allegedly murdered around her.

Despite suffering a bullet graze that fractured her skull, Cassidy managed to call police, identify the attacker and warn them he was headed to her grandparents’ house next, police say.

Police then intercepted Haskell, who has since been charged with capital murder in relation to the massacre.

Cassidy speaks out: “Stay strong”

Now, the lone survivor of the massacre  has spoken out for the first time since the horrifying event.

Cassidy, who was released from hospital on Friday, bravely spoke at a memorial ceremony on Saturday morning in her family’s honour — saying she’ll “be able to see them again one day”.

“I’m really thankful for all of the people who have been praying for me and keeping me and my family in their thoughts these past few days,” Cassidy said at the event, which was held at a local elementary school.

“I’m feeling a lot better, and I’m on a straightforward path to recovery.”

The teenager, whose voice only occasionally cracked during the moving speech, then quoted a passage from a Harry Potter novel that she’d found comforting.

“In The Prisoner of Azkaban, Dumbledore says, ‘Happiness can be found in the darkest of times, if one only remembers to turn on the light,” she said.

‘I know that my mom, dad, Bryan, Emily, Becca, and Zach are in a much better place, and that I’ll be able to see them again one day,’ she said.

Raising one hand in the air, she added “Stay strong!” — a phrase that has become a rallying cry for the shattered local community and Cassidy’s remaining family.

Cassidy, who is expected to make a full recovery, also helped release 600 colorful balloons into the air at the event: 100 for each slain member of her family, the Daily Mail reports.

The remarkable teenager was introduced at the event by her grandfather, Robert Lyon, who pointed out that her actions may have saved the lives of many others.

“Without her courage and quick thinking, we might be mourning the deaths of 20 — yes, I said 20 — people today including myself and nearly all of our children and grandchildren,” Lyon said.

Haskell , from Utah, appeared in court on Friday, looking dishevelled as a prosecutor read out details of the alleged crime.

He pleaded guilty to assault in a domestic violence-related incident in 2008 and was also the subject of requests for restraining orders by his mother and sister, the Daily Mail reports.

If you’d like to help Cassidy, her family has asked anyone wishing to help donate to the Cassiday Stay fund here.