Two years on from the unsolved killing of a baby girl in Auckland, the Herald can reveal a charge has been dropped against a family member accused of trying to obstruct justice.

Meanwhile, Manukau ward councillor and former police officer Alf Filipaina has issued a plea for justice for baby Sofia days ahead of the anniversary of her death.

"She needs to rest," Filipaina said.

He is calling on anyone with information to come forward.

"I don't how they're living with the fact they might know something."

Police believe Sofia Taueki-Jackson, aged 14 months, was killed at her mother's home in Flat Bush Rd, Clover Park, after suffering a catastrophic and unsurvivable head injury late on Saturday, May 23, 2020.

Several people were present at the property at the time.

Three days after her death, police launched a homicide inquiry, dubbed Operation Asbury.

No one has ever been charged with her killing. Her family has repeatedly declined to speak with media.

Detectives overseeing the case earlier said some of Sofia's family members refused to help police.

"Although a number have spoken to police, there are key members of the immediate whānau who were present but are refusing to assist the investigation," said Detective Inspector Tofilau Fa'amanuia Va'aelua, of Counties Manukau CIB.

"We are simply seeking the truth for Sofia. Tell us what you know, regardless of how insignificant it may seem to you."

Investigators believe some people with knowledge of the killing have provided actively misleading information.

A week before Christmas 2020 police charged a close relative of Sofia with attempting to obstruct the course of justice.

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The 25-year-old woman was a close relative of Sofia but is not her mother.

The case spent months in the Manukau District Court before the charge was quietly dropped.

Police said the Crown Solicitor at Manukau decided not to proceed further with the charge.

Neither police nor the Crown Solicitor's Office at Manukau would immediately comment on the reason the charge was withdrawn, ahead of a formal court process to release the Crown's memorandum involving input from the formerly accused's lawyer.

Detective Inspector Shaun Vickers, of Counties Manukau CIB, said Operation Asbury continues.

"No matter how much time passes, police remain committed to seeking justice for Sofia and holding the person, or persons, responsible for her death to account."

AUT law Professor Kris Gledhill said a Crown Solicitor must constantly assess if there is sufficient evidence a prosecution is reasonably likely to proceed, and that there is enough of a public interest to prosecute.

"The simple fact is that evidence often emerges which shows that one or other parts of the test aren't met any longer."

Professor Gledhill said sometimes police take a different view of the evidence than a Crown lawyer.

For instance, a lawyer may be more aware of how the defence could challenge the weight to be added to the evidence, which can undermine the prospect of a successful conviction.

A second issue is that further expert evidence can arise that undermines the value of the initial evidence, he said.

"So it often happens that the evidence available at the outset, when the police charge someone, looks less strong at a later stage."

Another legal point sometimes at play is the rule against double jeopardy, meaning people cannot be prosecuted to verdict twice except in very limited circumstances, he said.

But if a charge is withdrawn, double jeopardy does not apply and another charge, or the same charge, can be brought again down the line.