Andrew Lloyd, a former prisoner with a history of violence and drug abuse, murdered the 13-month-old baby of his girlfriend of just a couple of months.
An official review into Aaron Gilbert's death in May 2005 has found a catalogue of warning signs in the case which were not linked together.
It shows how the risk posed by Lloyd and Aaron's vulnerability came together without professionals being involved.
It says the public should also get involved in helping protect children.
For the first year of his life, baby Aaron lived with his mother Rebecca Lewis in an environment which "raised no concerns for his welfare", the official review by the Swansea Local Safeguarding Children's Board found.
But in March 2005 Lloyd formed a relationship with Aaron's mother and just weeks later Aaron was dead.
"At no time were they aware that Andrew Lloyd, Rebecca Lewis and Aaron Gilbert were living together"
According to the review, Lloyd was "a very troubled young man", the victim of physical abuse, domestic abuse and neglect as a child, who had grown into a man with a history of repeated offending.
He had two convictions for violence - although none involving a child - and had served a six month prison sentence for grievous bodily harm.
He had also made repeated suicide attempts - both seemingly linked to relationship issues - and was diagnosed with a personality disorder in March 2004.
At the same time, a problem with alcohol and drug abuse was also identified.
Crucially, the official review says, when Lloyd was released from prison - on licence in January 2005 - that information was not placed on the police national computer.
Although it says it is not clear where the fault for this lies.
Subsequently, when a court warrant was issued for Lloyd breaching his licence, because the original warrant was not placed on the police computer, that too was absent from the database.
The last police contact with Lloyd before his arrest for Aaron's murder was when he was admitted to psychiatric hospital in March 2005 after another suicide bid.
The review says following an assessment by police, a decision not to hold a multi-agency conference - which would have combined police, probation, psychiatric services and social services, was taken
The review said that was the last time before the baby's murder that agencies "with significant information about Andrew Lloyd" might have become aware of each others work and come together to address the risks he posed.
Shortly after Lloyd began a relationship with Aaron's mother and the baby's short life was to tragically end.
Again, the review says although professionals from various agencies had seven contacts over Aaron "at no time were they aware that Andrew Lloyd, Rebecca Lewis and Aaron Gilbert were living together".
In the next few weeks Aaron was taken to the GP and the local hospital A&E department although Rebecca Lewis took him home before he could be seen.
A number of failings by social services were then identified in the case - including a home visit to check up on Aaron not taking place because of sickness.
But the review stresses "the piece of information which all agencies lacked which might have led to the consideration of the safety of Aaron Gilbert was the presence of Andrew Lloyd in a parenting capacity in relation to him".
The serious case review concludes that all agencies involved in the case have lessons to learn, something which they in turn have acknowledged.
It says there were opportunities for the services working with Lloyd to exchange information and make an assessment of the risks he posed to the public.
Instead Lloyd's licence was not placed on police national computer, concerns about his mental health and personality disorder were not shared outside of adult mental health services
Lloyd's history of domestic violence was not shared with the probation service, and the probation service un turn did not share information on him with social services, the police or adult mental health.
The review also highlights the role of the community in helping to spot abuse.
On at least two occasions before Aaron died, injuries were spotted but went unreported.
When a report was made, it lacked vital information such as Lloyd's involvement and the baby's correct address.