Two of the seven accused in the Tembisa gang-rape trial have been linked to the crime scene through DNA.
The semen of Kabelo Mawale, 23, and Bongani Nhlapho, 21, was found on the sheet of the bed on which the victim claims to have been raped.
Forensic analyst Inspector Inge Taylor said she was given blood samples of all the accused, the victim's vaginal swab and the sheet to examine.
"The stains on the sheet matched the DNA of Bongani and Kabelo," she said.
But Taylor told the South Gauteng high court that no DNA could be found on the victim's vaginal swab, possibly because there had been no ejaculation, a condom was worn or the rapists had ejaculated outside of the vagina .
She also said that it could be difficult to find the semen of all the perpetrators.
"One can find mixed DNA and the semen of the person who penetrated last is often more present," she said.
Mwale, Nhlapho, and co-accused Sello Mohlala, Thabiso Thukwane, Oupa Mohlala, Moeketsi Mphuthi and Mojalefa Seleka allegedly gang-raped the woman in 2005.
The woman, known only as Buyisiwe, testified that she was at her friend's home when the group broke in and raped her at gunpoint. She said they took her to a squatter camp where they raped her again.
The accused have denied raping her , saying she was a prostitute who agreed to have sex with them for money.