"He said if I screamed, he would shoot my grandmother," the 15-year-old girl told the High Court, sitting in the Palm Ridge Magistrate's Court in Alberton.

She was testifying in the trial of Johannes Jacobus Steyn, dubbed the "Sunday rapist".

She explained how she, 11 at the time, walked to a shop with her four-year-old brother and grandmother in Rustenburg on November 11, 2008 when a white bakkie stopped next to them.

A man with a cap and sunglasses asked her name and then pointed a gun at her grandmother. He grabbed her arm and pulled her into the vehicle over his lap, she said.

"He tried to close the door and pull away at the same time. I kicked the door. That's when I fell out."

She tried to put her glasses back on to see if the bakkie had a number plate, but it drove off.

During cross-examination Anton Lerm, for Steyn, asked the girl whether she was compelled to testify.

"No, I was not forced to testify."

Steyn is charged with two counts of murder, 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 pleaded not guilty to all 37 charges against him. The murder charges relate to the deaths of schoolgirls Louise de Waal and Lazanne Farmer.

Seven of his alleged victims testified during his last appearance.

Most were aged between 15 and 18 when he allegedly forced them into his bakkie at gunpoint on Sunday mornings between 2008 and 2011, drove off with them, and raped or sexually assaulted them.

Earlier a forensic cellphone expert from Vodacom testified on the GPS co-ordinates of a cellphone registered in Steyn's name. The phone was linked to the locations where his alleged victims were attacked.

When questioned on the cellphone towers' accuracy in determining location, Petrus Prinsloo said it could not be out by more than 100m.

"The percentage will be very small."