A couple accused over the death of their 11-week-old daughter were caught by police listening devices "coaching" their other child on how to answer questions about it, a court has heard.

Officers investigating the death of Tahani Mahomed bugged the South Auckland home of her parents, Azees Mahomed, 31, and Tabbasum Mahomed, 26 - hiding the first bugs on the day of the girl's funeral.

Tahani was admitted to hospital with severe head injuries in December 2007, but the South African-born couple were unable to explain how she had been hurt.

Azees Mahomed, her father, is accused of murder and two counts of causing his baby grievous bodily harm - in one instance breaking her leg by apparently twisting it violently and in the other by inflicting head injuries that caused brain damage.

He faces an additional charge of failing to provide the necessaries of life. His wife Tabbasum is also accused of this, but is not charged with murder.

Crown prosecutor Phil Hamlin told the High Court at Auckland yesterday that after a police officer told the Mahomeds they would have to attend a family group conference with their daughter Tasmia to discuss what had happened to Tahani, they were heard talking about "coaching" her.

"You will hear the two of them coaching her so she doesn't make incriminating statements about them," he told the jurors.

On audio tapes which had been translated from Hindi, they would hear Azees Mahomed say, "We'll have to do it by Monday", before commenting on the questions Tasmia was likely to be asked.

Mr Hamlin said Tabbasum Mahomed would be heard saying, "They will question Tasu [Tasmia] about what happened to Tanu [Tahani] ... who hit/killed her."

Azees Mahomed was recorded saying he knew police had "one big proof against us" because they knew the baby had been left in a car during a hot day, and knew of another incident where her nappy wasn't changed for an entire day.

Defence lawyer Chris Wilkinson-Smith said Azees Mahomed denied ever harming Tahani. A police interview would show he was distressed after being told she might die.

Mr Wilkinson-Smith told the jurors the Crown case relied heavily on the taped conversations. "In the end you will decide what to make of these conversations. They are ambiguous and in some cases support the innocence of Mr Mahomed."

Some words were missing in crucial passages and they weren't in English, he said.

Tahani was admitted to hospital on December 28, 2007. She died on New Year's Day and her funeral was on January 3, 2008.

Mr Hamlin said the baby's head had been forced violently against a hard, "unforgiving" surface.

When examined, her breathing was shallow and irregular, her arms and legs were extended abnormally and the soft area on her head was bulging. She was also malnourished and weighed only 4kg.

An autopsy revealed her retina had detached, her skull was fractured and there was nerve damage to her spinal cord.

The Crown said the injuries could only have been caused non-accidentally, through rapid acceleration and deceleration.

"All of them happened at the same time, within a few shakes and a few hits of each other," Mr Hamlin said. "Baby Tahani was shaken or slammed against a hard surface."

The prosecutor said the infant couldn't have caused the injuries to herself - she "wasn't even running around to cause them".

She had been killed by someone else.

"This was a vulnerable baby, who couldn't defend herself, who was killed by a violent assault."

One day, he said, police had been called after Tahani was seen to be "effectively cooking" in a car. The call had come from a passerby, who told Azees Mahomed not to leave when he returned. But instead, he wiped sweat off the baby's head and drove off.

Another time, she was said to have been left in a dirty nappy for much of the day.