Joost van der Westhuizen's private investigator has revealed that two policemen are behind the sex tape blackmail campaign against the former Springbok scrumhalf.

Mike Bolhuis also confirmed that Van der Weshuizen is taking legal action against the two.

The security expert cleared the scrumhalf of any involvement in the tape and said he passed a polygraph test with flying colours.

Bolhuis said he knows who is behind the video.

"One is still with the cops. The other one is out. We cannot divulge any of those names because it will obviously be presented in the court of law on the criminal charges...they were the producers of the video," said Bolhuis.

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