It was not the first time the little girl had seen her father attack her 21-year-old mother. In the two years before her murder, at least 11 incidents of abuse and domestic violence by Williams had been reported to Nottinghamshire police by Brittle, her friends, neighbours and family. None resulted in criminal charges. Some of the desperate calls for protection were not even followed up.
On Tuesday, the Independent Police Complaints Commission revealed that, despite those repeated pleas for help, Nottinghamshire police had failed to take even the most basic of steps to protect Brittle and her daughter.
In a scathing report, the IPCC revealed it had recommended that 10 officers face disciplinary charges, including misconduct, after the young mother was "significantly let down by systemic failures" in Nottinghamshire police service.
Six officers pleaded guilty to misconduct in relation to Brittle's calls for help. No further action was taken against two of them, while three received "management action" and the sixth was given a written warning. Four other officers were subject to unsatisfactory performance procedures, a lower level of disciplinary action taken against officers whose behaviour is considered to be "at the lower end of the scale, such as lateness or rudeness", said an IPCC spokeswoman.
That Nottinghamshire police was also found guilty of systemic failures was "all the more horrifying", said IPCC commissioner Amerdeep Somal, who led the investigation, because two years before Brittle's death, another attack by an estranged husband on his former partner had revealed very similar flaws. That case had forced Nottinghamshire to admit its domestic abuse policy was "not fit for purpose".
The policy was removed from circulation but no substitute document was issued until March 2010 and, the IPCC investigation into Brittle's murder discovered, officers whose lack of knowledge had contributed to the 2008 incident were given no further training in domestic abuse.
The IPCC said the same culture of ignorance around domestic abuse was still widespread across Nottinghamshire police force. "The systemic failures … were compounded by the fact that the force had previously been warned about many of the same issues," said Somal.
"In this case it is clear that a number of officers failed to perform to the level expected of them and basic actions that may have helped others see the full picture of [Brittle's] suffering were not completed. However, it is clear that beside the failings of individual officers, Casey was significantly let down by systemic failures within Nottinghamshire police."
The IPCC investigation reported that on 3 October 2010, Brittle's daughter was heard crying and screaming at her home in New Basford. A next-door neighbour was said to have heard the child screaming: "I want my mummy." It was later established that the little girl had walked into the room four times to find her father carrying out the murder.
After her father left the house and her mother lay unconscious next door, the child was left alone in her bedroom for two hours. She is now being cared for by relatives. Williams was convicted of murder in March 2011 and sentenced to life imprisonment.
Despite admitting that "members of the public will no doubt be shocked by the findings of this investigation" and that "it may mean that victims may hesitate to report domestic abuse to the police", Somal said his investigation had failed to establish "with certainty" that "if officers or the force had served Casey better then she would still be alive today".
He said: "Williams was a violent offender with scant regard for the law. It is impossible to judge what impact any positive action taken by the force would have had on him and his attitude to Casey."
Brittle's mother, Victoria Blower, agreed. Describing her daughter's death as "the absolute worst day of my life," Blower said: "I know mistakes were made in dealing with previous attacks involving Casey, but there is only one person responsible for my daughter's death and that is Sanchez Williams.
"Maybe one small change in the way things were handled could have saved her, or maybe Sanchez Williams was a timebomb just waiting to explode and nothing that anybody could have said or done was ever going to prevent him from murdering Casey."
Blower praised Nottinghamshire police for the "positive action" they have taken since Casey's death. "I am glad to have been involved in their work to improve the handling of incidents of domestic violence," she added. "I would also urge people not to close their own eyes and ears if they see or hear somebody experiencing domestic abuse, but to pick up the phone and call the police. You never know, it might be your call that saves a person's life. It is too late for my beautiful bubbly girl, but don't let it be your daughter, neighbour or friend who is next."