The way a police force handled a man who went on to murder his partner's 13-month-old son is to be investigated.
Aaron Gilbert had suffered 50 injuries from head to foot
It follows complaints by Aaron Gilbert's father who is also unhappy about the lack of information he received before Andrew Lloyd's trial.
Aaron's mother Rebecca Lewis was jailed for six years for familial homicide.
South Wales Police said it would cooperate fully with the Independent Police Complaints Commission (IPCC) investigation.
Aaron's father, Gareth Gilbert, has also complained that Lloyd's details were not put into the Police National Computer.
Lloyd, 23, from Swansea, was jailed for a minimum of 24 years after admitting murdering Aaron, who died from brain damage in May 2005. He had suffered 50 injuries.
At the trial last October, Swansea Crown Court heard Aaron had been so badly beaten by his mother's boyfriend he looked "like the Elephant Man".
When Lewis was found guilty of familial homicide for failing to protect her son, she became one of the first in the UK to be convicted of the new offence which had become law in May 2005.
Andrew Lloyd and Rebecca Lewis were jailed in December
Responding to the announcement of the IPCC investigation, South Wales Police Assistant Chief Constable David Morris said a "lengthy and complex investigation" into Aaron's death had resulted in the convictions of Lloyd and Lewis.
Lewis' conviction had been the first such prosecution in Wales, he said.
He said a serious case review had "acknowledged that many of the safeguards put in place to identify vulnerable children worked effectively".
Steps had been already taken to follow up several recommendations from the report, he added.
He said the force had recorded Mr Gilbert's complaint, received via the IPCC, and promptly referred it back to the watchdog.
Tom Davies, IPCC Commissioner for Wales, said: "This was a despicable crime and Aaron's father has suffered a terrible loss.
"Mr Gilbert, from Swansea, has made a number of complaints about South Wales Police and I have decided that this matter warrants an independent investigation."
An official review into Aaron's death found a catalogue of warning signs in the case which were not linked 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.
In July, the Court of Appeal, which heard Lloyd treated Aaron "like a punchbag", rejected his application for leave to appeal against his jail sentence.