One of the men accused of raping a girl believed to be mentally impaired was released by the Roodepoort Magistrate's Court on Wednesday, their lawyer said.

Speaking outside the court, because proceedings were closed due to the appearance of minors, attorney William Karam told the media he had been released because of a lack of evidence.

Two others - an 18 and 19-year-old - were released on R1500 bail.

The matter was postponed to September 6.

Seven people, including four minors, were arrested in Dobsonville, Soweto on April 17, after they were matched to descriptions of people seen in a cellphone video recording of a gang rape.

The video of the 17-year-old girl being raped went "viral" on the internet on April 18, and was one of the main topics trending on social networking site Twitter.

Two of the minors also implicated in the case appeared with the three adults.

A third minor was not present in court because he was writing his Grade 12 mid-term exams. His probation officer had confirmed this to the court, said Karam.

Two of the minors are 16-years-old. The third is 17.

A 13-year-old was appearing in a separate court room.

He was undergoing psychiatric evaluation to determine his criminal capacity.

Karam said the evaluation had commenced, but would take another month before it was concluded. - Sapa