A lawyer for one of the two accused men said Terreblanche tried to have sex with at least one of the defendants.
Mr Terreblanche's body was found on a bed with his trousers pulled down.
Police had initially said the killing was over a wage dispute, but are now exploring the possibility that the killing was an act of self-defence.
"We are not going to focus on one thing," said Musa Zondi of the Hawks, South Africa's elite criminal investigation unit, which has taken over the investigation.
"We will investigate all pertinent facts that have a bearing on the matter."
Gen Jan Mabula, head of the Hawks in North West province confirmed to South Africa's City Press newspaper that the suspects' clothes had been sent for forensic examinations.
Terreblanche was discovered at his farm in Ventersdorp on 3 April after having been beaten to death.
Two black farm workers have been charged with his murder.
Puna Moroko, the lawyer representing one of the accused men - 28-year-old Chris Mahlangu - told South Africa's Sunday Times newspaper the attack was triggered by a sexual assault.
"My instructions from my client are that there was some sodomy going on and it sparked the murder of Mr Terreblanche," he said.
The lawyer representing the other defendant - a 15-year-old boy who cannot be named - made no comment on the sodomy allegations.
Mr Moroko claimed the accused men were given large quantities of alcohol before Terreblanche allegedly tried to have sex with "one or both of them".
Terreblanche was leader of the Afrikaner Resistance Movement (AWB), a white supremacist group, and believed firmly that whites and blacks should be kept apart.
AWB spokesperson Andre Visagie strongly dismissed the sexual assault allegations.
"The media must choose now whether they want to regard Terreblanche as a racist or as the rapist of a black youth," the City press newspaper quoted him as saying.
BBC News
