He sobbed as she described a phone call he made to her on the day teenager Louise de Waal was murdered in October 2010.

"He phoned me and said he kidnapped another girl. He is sorry and that he is a monster," she told the High Court sitting in the Palm Ridge Magistrate's Court in Alberton.

The court ordered that the ex-wife not be identified. She gave evidence in camera.

Steyn is being tried for the murder of schoolgirls De Waal and Lazanne Farmer.

Steyn is also charged with 11 counts of rape, 10 of sexual assault, 10 of kidnapping, one of attempted sexual assault, one of attempted kidnapping, and two of assault. He has pleaded not guilty to all the charges.

His ex-wife said he phoned her on October 12, 2010, the day of De Waal's murder, and told her he had kidnapped a girl.

He told her he was confused and he was going to leave. He said there would be police at his house and that she should tell them he was guilty.

Asked about his whereabouts on Sundays, she said he did community service at a hospital in the mornings for almost four hours for a previous conviction.

"It's what he told me."

Throughout his ex-wife's testimony, Steyn cried. He put his head in his hands, sighed, and constantly wiped his eyes.

When asked why he always brought a Bible into court with him, Steyn said: "It gives me courage".

He said his brother gave him the Bible in 2007. Steyn said Psalm 43, especially, gave him courage.

The Psalm reads: "Judge me, O God, and plead my cause against an ungodly nation: O deliver me from the deceitful and unjust man."

He kept a bookmark with a picture of his wife and child on that page.

The 11 girls Steyn allegedly attacked between 2008 and 2011 were aged between 11 and 18.

Two of Steyn's alleged victims testified in camera on Monday.

An 18-year-old recounted how her friend jumped to her death from a moving vehicle in an attempt to escape.

"She let go of my hand and jumped out of the bakkie," she told the court.

The fleeing teenager, Farmer, did not survive.

"I wanted to jump out with Lazanne, but then he grabbed me and closed the door," the 18-year-old testified.

"I thought she was going to get help. I though she might have gotten hurt."

The two girls were kidnapped on September 5, 2010, in Pretoria.

The 18-year-old testified that her disguised kidnapper drove her to a remote location and raped her. He kept her sandals and her bra.

Another 16-year-old also testified about being kidnapped, blindfolded, and sexually assaulted.

She told the court that when he undressed her, he saw she was menstruating. "He told me it was my lucky day."

He then took out a "machine" and moved it around her breasts. She explained how he used this "machine" to sexually assault her.

Her kidnapper, disguised in a wig and sunglasses, kept her hairband, her purple T-shirt, her underwear, and her shoes.

Relatives of Farmer were in court on Monday. They cried during the 16-year-old's testimony.

Her mother Anna Farmer briefly took the stand.

"For me, it still feels like it happened yesterday," she said, crying.

The trial continues on Tuesday.