A mum killed herself and her four-year-old son in a fire after losing a custody battle.
Janma Joshi, 40, had been ordered to hand over son Jai to his father Paresh Patel, but instead used petrol to set her home on fire. Their bodies were found by firefighters.
Her husband Mr Patel, 43, told the Liverpool Echo: "I think she felt if she couldn't have Jai, no one could. She knew how important he was to me.
"As a father, you never expect your child to die before you. However, my son Jai died at the hands of his so-called mother and she knew exactly what she was doing.
"There is only one way to describe this – evil. As soon as they told me, I knew she had done it deliberately.
"She knew the way to hurt me was through Jai. Ultimately, Jai paid the price."
He claimed Mrs Joshi had kept Jai at home in Tuebrook, Liverpool, for two weeks after an access visit - despite him being granted custody over fears for the boy's 'emotional wellbeing'.
Mr Patel, from Preston, Lancashire, said: "I sent the social worker a message saying they needed to get Jai out of that home and I notified the authorities numerous times."
The matter will be passed to the Lancashire Safeguarding Children Board for consideration by their serious case review panel.
Jane Booth, the independent chairman of the Lancashire Safeguarding Children Board, said: "My heart goes out to Jai's family and friends.
"This is a very distressing case. The circumstances of Jai's death have been referred to our serious case review group for consideration.
"Any review we complete will be published and any issues about the way in which children and their families are supported and safeguarded will be addressed."
A spokesman for Merseyside Police, said: "Our thoughts are with the family at this time and they can rest assured that Merseyside Police will co-operate fully with Lancashire Safeguarding Children Board in relation to any future serious case review.
"The full circumstances of what happened are currently being reviewed and will be considered both at an inquest and by the Lancashire Safeguarding Children Board.
"It would therefore be inappropriate to comment any further at this stage."