In July 1992 a young mother, Rachel Nickell, was stabbed repeatedly and killed on Wimbledon Common in London. She was with her son, Alex, who was just two years old. He was the only witness.
Now aged 27, Alex Hanscombe has spoken to BBC Woman's Hour about that time and how he has moved on.
"More than anything, I remember just after the attack reaching out to my mother and asking her to get up. I realised in a split second that she was gone and wasn't coming back."
Alex's memories about the attack are vivid. He recalls the assailant washing his hands in a nearby stream. He also remembers seeing a cash receipt which had fallen from his mother's pocket - he rested it on her forehead.
It took many years for the killer to be caught.
A man called Colin Stagg was wrongly accused of her killing and a judge criticised the police investigation which deployed a "honey trap".
In 2008 a man called Robert Napper pleaded guilty to manslaughter on the grounds of diminished responsibility. Napper, who had schizophrenia, had already been convicted of a 1993 double killing. He is at Broadmoor high security hospital.
There was intense media interest in the case, so Alex's father, Andre, took him to rural France to start a new life.
After a while the press found out where they lived, so they moved once more - this time to Spain.Image copyright Alex Hanscombe Image caption
People knowing where they lived presented a risk to Alex's life. He was the only person to have witnessed his mother's killing and for as long as the killer was at large, he was in danger.
He insists that he was never scared, although he acknowledges that "my life could have ended that very morning".
He says certain situations used to trigger very strong reactions in him as a child, especially if he saw someone who looked like his mother's killer.
Alex has always strived not to be defined by what happened.
"There were all sorts of claims that were made about me, such as I'd never talk again, I'd end up living under a bridge or even repeat the same cycle of violence. But it's about creating your path and living your own way," he said.Image copyright PA Image caption
He has recently returned to the spot on Wimbledon Common where his mother was killed.
"I had this strong urge to go back there and something magical happened.
"I knelt down and said a prayer. I said thank you for all my blessings and for making the pieces of the puzzle come together in the right way. And at that very moment I heard someone call, "Molly, Molly".
"I thought I was dreaming but it was a man calling out to his dog, Molly."Image copyright Alex Hanscombe Image caption
Molly was the pet dog with Rachel and Alex when she was attacked 25 years ago.
"The coincidence and this happening: it's all there for a reason," he says.
Alex lives in Barcelona with his father. He studies hypnotherapy, handwriting analysis and yoga.
He has written a book, about his mother and his life, called Letting Go: A true story of murder, loss and survival.