The elderly couple, who have taken 80 children into their semi-detached home in South Wales, said the teenager was ‘far and away’ the worst, as he sought out ‘weaker and more vulnerable’ children to victimise.
They said the teen was murder obsessed and had a ‘cruel streak’ which saw him stamp on one girl’s toes after she had just had an operation on them, before allegedly pulling up the neighbour’s dogs legs following surgery and spraying deodorant in its eyes.
He also took two younger girls to a park to play a game he invented called murders.
The boy was found guilty of murder yesterday alongside Logan’s mother Angharad Williamson, 31, and his stepfather John Cole, 40.
They abused and killed the five-year-old before dumping his body in the River Ogmore, near their home in Pandy Park, on July 31 last year.
Speaking today, the teenage killer’s former foster carers said he would run around singing ‘kill the Jews’, which social services allegedly shrugged off as ‘banter’.
The foster father said: ‘It is the first time I’ve ever been worried about my own family – we are foster carers not psychiatrists.’
It was the only time in their 50 years of fostering that the couple have called social services to say they could not cope with a child’s behaviour.
The foster dad added: ‘We were frightened in our own home, we didn’t feel safe. I wanted him moved.
‘I told social services: ‘I want him out of here’ but the social worker turned it around on us saying we needed more training.
‘I was angry, we’ve been looking after children for all these years. We know what we are doing.’
The youth, 13 at the time, made a death threat against Logan while he was fostered with the couple for eight weeks.
The boy’s foster dad said: ‘He was always on about killing people – then he said he wanted to kill another boy.
‘I told social services – that should have rang alarm bells.’
The foster dad said: ‘Before he left us I said to myself that he was going to do something bad.
‘But I didn’t expect it to be murder or for it to happen so soon.’
The couple told how the boy terrorised them and other children in their care who he would pick on for fun.
The foster dad said: ‘He would be marching around the place singing ‘Kill the Jews’ – it was not natural.
‘When we told social services they said it was just banter but that’s nonsense.’
While staying with the foster family the boy went to a nearby park with their two younger granddaughters.
The foster mother said: ‘He told them they were going to play a murder game and they would be put in black plastic bags. We were shocked to find out that is what happened to Logan.’
The dedicated couple were warned the teenager had ADHD and autism when he moved in with them.
On his first night they found knives hidden around their house. One was a sharp Jamie Oliver vegetable knife, the couple still have no idea where he got them from.
He targeted weaknesses in other children staying at the house, deliberately stamping on the feet of a girl who had just come out of hospital after an operation on her toes.
The foster mum said: ‘We’ve had lots of smiles and laughter with all our children over the years. But there have been tears too, some of them have been very difficult.
‘Social Services told us the boy would be a challenge but this was way beyond anything we’ve ever experienced before.
‘We were told he’d be alright because he was on medication but it was like living with a little monster.’
The boy refused to wash and would play on his X-box round the clock in his bedroom, disturbing the rest of the household.
The foster mum said: ‘He wouldn’t even stop to go to the toilet – he had an empty coke bottle next to him so he could carry on playing.
‘He wouldn’t shower, the odour coming off him would take your breath away. ‘I’d say come on now go in the shower you stink.
‘He said he liked girls and I told him he wouldn’t get a nice girlfriend smelling like that. But he didn’t want to know.’
The boy went to a local comprehensive school while staying with the couple but was regularly excluded for being abusive to teachers.
He also shocked the foster family by painting his face and body bright blue like the aliens in the science fiction film Avatar.
The foster mum said: ‘That was weird – to get him the shower at the best of times was difficult, I had to gradually get him in there to get the paint off.’
They believe the teenager picked on other children in the home out of jealousy and he always wanted to be the centre of attention.
The couple have questioned whether he acted in the same way with Logan.
The foster mum said: ‘Normally children have triggers, you get to know what will upset them. But that boy didn’t have triggers, anything would set him off and then he wouldn’t stop.’