Steenkamp’s lawyer Dup de Bruyn was also inside the court room, as was cellphone records expert Captain Francois Moller.
A throng of journalists began entering the courtroom at 8.23am.
Police investigating officer Vineshkumar Moonoo and Captain Mike van Aardt were also present.
Pistorius, 27, is accused of murdering his girlfriend Reeva Steenkamp at his Pretoria home last year. He faces charges of premeditated murder and contravening the Firearms Control Act in a trial which is expected to last at least three weeks.
The proceedings in the wood-panelled courtroom will be broadcast live on television and radio, with the initial indictment listing 107 witnesses to testify for the State. The trial was due to start at 10am.