The father of nine-year-old Aria Thorpe has described the acquittal of the 16-year-old boy accused of her murder as a "robbery of justice," revealing that his other children now fear the boy could appear at their home.

Aria died on December 15 last year in Weston-super-Mare, North Somerset, after being stabbed in the chest. The 16-year-old boy, who cannot be named for legal reasons, was found not guilty of murder and manslaughter by a jury at Bristol Crown Court on Thursday and was released.

"We feel that the trial was a robbery of justice. We don't understand how you can stand up in court, admit to stabbing Aria, claiming she wasn't to blame, it was me 100 per cent but walk out the court a free man," Tom Thorpe, Aria's father, told the Daily Mail. He added that his daughter's sister fears the boy might approach their home, as there are no restrictions on his movement.

Thorpe expressed distress over how to explain the verdict to his older children, aged 14 and 11. "We can't get our heads around any of it. What example does this set to children across the country?" he asked.

During the trial, the defendant testified that he had intended to scare Aria. He described picking up a 21cm blade knife from near the kitchen sink before entering the lounge. He stated he waved the knife, intending to make Aria flinch, but admitted, "The knife went into her. Then I pulled it out. I didn't know what to do. She put her hand to her chest."

Court proceedings indicated that the teenager left the scene without checking on Aria or calling for help. He later told a group of children at a railway station that her death was an "accident." One of these children contacted the police, reporting that the boy had said he stabbed her and she was dead.

The boy later told officers, "I didn't use a lot of force, but it was a big knife. I don't know why I did it, it just happened… I walked over and stabbed her. She fell to the floor."

Aria's family has described her as "full of energy, curiosity, innocence and happiness." Her father recalled a "magical" family trip to Disneyland. Her mother, Victoria Hull, provided a statement to the court detailing their last moments together, making pizzas and watching television before Ms. Hull left for her evening work shift.

In response to the verdicts, Aria's aunt Katie Thorpe questioned the meaning of justice and the message it sends to society. "What does it teach people when a child can lose her life in such a horrific and senseless way, yet nobody is held accountable?" she asked. Great aunt Sarah Cox Pike added that the verdict felt like a failure of the justice system.

The family plans to obtain court transcripts to instruct a barrister to review the proceedings for fairness and accuracy.