A secret witness told the court she overheard Ms Guode tell a relative she feared she would die and "she did not want the kids to go to [her husband] and the wife, that she wanted herself and the kids to go together, to end it".

Ms Guode, 36, drove her car into Lake Gladman on April 8, 2015, killing baby Bol and his twin four-year-old siblings Hanger and Madit. Ms Guode is charged with their murder.

She is also charged with attempting to murder another of her children, Aluel, who was also in the car but survived.

The prosecution's case on Friday featured a witness whose identity cannot legally be revealed.

The witness had allegedly faced threats from Melbourne's Sudanese community, who were aware of their plan to testify.

Initially the witness did not arrive at the scheduled court video-link on Friday morning, and a warrant was issued for their arrest.

When the witness was eventually arrested and brought before the court via video link, their testimony was explosive.

"[Ms Guode] was saying the wife had been giving her a hard time, threatening her, calling her and saying she was going to get a witchcraft doctor to kill her or make her leave her husband or kill the kids," the witness said in a statement tendered to court.

"Akon said she was scared and [a community member]  said not to worry, it's bullshit, don't believe her and that it wouldn't work in Australia".

"I could see that Akon was stressed and scared. Akon said she would rather take her own life and that of the kids. She said in a jealous kind of way that she did not want the kids to go to [her husband] and the wife, that she wanted herself and the kids to go together, to end it".

The witness said they saw Ms Guode again after the children had died.

"I told her, 'did you really do it'?"

"She said 'Yes, I did it. I did not expect to still be alive'."

"She was not showing any remorse. I was getting annoyed so I just left."

The witness said Ms Guode was the "cultural wife" of  Joseph Manyang, who the witness called "Mayur", and with whom she had four children. This was a Sudanese tradition, as Mayur was the older brother of Ms Guode's deceased husband. Ms Guode also had three other children to her deceased husband.

The witness said that in Sudanese culture if your husband dies, you are required to marry the older brother.

But Mayur already had a wife, and this caused escalating tension, the witness said.

Mayur mainly lived with his normal wife, but sometimes spent time with Ms Guode, and their four children, -  three of whom perished in the lake.

"There was a lot of jealously and anger. Even the elders tried to sit them down and get it sorted but it did not work. I think that it was a love triangle. I think it was part Mayur's fault. He should have just been with one wife. But Akon should have stopped having more children with Mayur as well."

The witness said at one party Mayur's wife came and slapped Ms Guode across the face. The witness also said Ms Guode had an intervention order out against the wife.

On the morning the children died Ms Guode had been visited by a member of the Sudanese community over a large debt that Ms Guode had helped facilitate, the witness said.

Ms Guode was in charge of collecting money for the debt, and her house was filled with piles of cash - she told the witness $64,000. But the whole debt was to be for $80,000, and Ms Guode said she hadn't been able to collect all the money, the witness said.

Magistrate Carolene Gwynn ordered all members of the public, including a large Sudanese contingent, out of the court before the witness gave evidence, due to claims from the prosecution that the witness was being threatened by members of the Sudanese community about giving evidence.

Ms Gwynn must determine whether Ms Guode stands trial. The hearing will resume on Wednesday.