The summary report, made public at a news conference at The Rep Theatre in Birmingham this morning, said there were delays in producing assessments and reports and in establishing Toni-Ann's immigration status, which affected the quality of decision making.

The review - carried out by David Lambert, a former assistant chief inspector at the Social Services Inspectorate - concluded that the failings highlighted "the need for professionals to maintain a thoroughly watchful and diligent stance in respect of their safeguarding obligations to the children and young people in their charge".

DNA testing in post-mortem examinations revealed that Mr Byfield was not the biological father of Toni-Ann.

The killings took place in what is thought to have been a drugs dispute which Byfield - who had served a nine-year jail sentence for drug dealing - was involved in.

Detectives believe Toni-Ann was shot as she ran away to stop her identifying the killer, while Byfield was shot in the chest.

No one has been charged in relation to the murders.

Ruthless cartel

Detective Chief Inspector Neil Basu said that Byfield was "closely affiliated" to a group of Jamaican crack dealers running cocaine between the UK and Jamaica.

"I know that this is a ruthless and organised cartel," he said. "I believe that the murderer came from or is known to members of this gang.

"It is possible that Tony was trying to elevate himself within the hierarchy of this gang or was trying to call in a debt on their behalf and was killed as a result of his actions.

"I know he was owed £25,000. I need to know the identity of the man who owed him that money."

A reward of £20,000 has been offered for the identification, arrest and prosecution of the person(s) responsible.

Anyone with information should call the incident room on 020-8733 4704 or Crimestoppers on 0800 555 111

Toni-Ann Byfield inquiry: reaction in quotes  Guardian UK