Speaking to the Sun, Mary O'Connor, 60, questioned the timing of his release - just two days after the anniversary of tragic Peter's death.
She said: 'The fact he is being freed so close to the anniversary is a cruel twist of fate. To think he will be walking the streets again is horrifying. He is a danger to society and especially children.
'He is a nasty piece of work and if he had a compassionate bone in his body, he could have saved Peter.'
Thirty-nine-year-old Owen has served little over two years for his part in Peter's death. The little boy's mother, Tracey and her boyfriend, Steven Barker, are still imprisoned.
Mary added: 'I hope the guilt is tearing Owen apart because he hasn't been properly punished. I'd like to think he will spend the rest of his life haunted by Peter's death. But I doubt it.'