Magistrate Deon Schnetler ruled the defence failed to prove that the release of Sergeant Nandi Nkosi and Zoe Biyela would be in the interests of justice.
The two women are charged with conspiracy to murder, possession of unlicensed firearms, possession of unlicensed ammunition, possession of stolen vehicles, and theft.
In affidavits, both women have denied involvement in the alleged plot to kill forensic investigator Paul O’Sullivan and crime intelligence officer Colonel Nkosana “Killer” Ximba.
Schnetler said there were discrepancies in the women’s statements that cast doubt on their claims that they were not involved in the alleged plot.
He said Biyela was in the hotel room in Rivonia, Johannesburg, where the plot was discussed and appeared to have been part of those discussions.
Both women could also try to interfere with witnesses and possibly try again to carry out the planned crime if released on bail, Schnetler said.
At their last appearance on Friday, prosecutor Lawrence Gcaba said the State opposed bail because the women were facing serious charges.
“The State has a strong case against the accused,” he said.
He described Nkosi as “dangerous in terms of her skills” because she knew the witnesses and had the means to track them down. She allegedly provided software for tracking the investigators.
Nkosi has been suspended from her job with the crime intelligence unit.
Titswa Modise, for Biyela, said she was unaware of the plot to kill the investigators.
“The case against the accused is exaggerated and does not exist,” said Modise.
Biyela, Nkosi, and their co-accused Siboniso Miya, Owen Serrero and Jacob Nare will appear in court again on February 18.