The athlete known globally as Blade Runner has admitted to shooting Steenkamp three times through the bathroom door of his Pretoria home during the early hours of 14 February 2013.
Prosecutors argue that it was an act of premeditated murder by the South African. Pistorius claims he shot model Steenkamp in the mistaken belief that she was an intruder.
The 27-year-old’s fate will be decided not by a jury but by a female judge, Thokozile Masipa, who has a reputation for handing out stern sentences for crimes against women.
Pistorius, who became the first double amputee to run in an Olympics at London 2012, was granted bail 12 months ago after a lengthy and eventful initial hearing.
One South African broadcaster is dedicating 24-hour rolling coverage to the trial of one of the best-known names in track and field, though only some of the courtroom action is allowed to be shown.
Pistorius asserts that he did not have time to put on his prosthetic legs and was therefore on his stumps and feeling vulnerable when he fired the shots that killed Steenkamp.
The state disputes that version of events, saying Pistorius was wearing prosthetics and shot his girlfriend, who was cowering in the bathroom, following an argument.
Prosecutors and the defence also differ on whether the bedroom light was on in Pistorius’s house. He claims it was pitch dark, and he therefore did not realise Steenkamp was not beside him in bed.