Pistorius has said he thought there was an intruder in his home and pleaded not guilty to murder.
A key part of the prosecution's case was its assertion that Steenkamp screamed during a late-night alleged fight with Pistorius before he killed her. But Masipa said some of those witnesses who testified to hearing a woman scream were "genuinely mistaken in what they heard, as the chronology will show."
Masipa also cited testimony of an acoustics expert called by the defense, saying it cast "serious doubt" on whether witnesses who were hundreds of meters (yards) away in their homes -- as some state witnesses were -- could have differentiated between the screams of a man or a woman.
Earlier, Masipa began by outlining in detail the four charges against the Olympic runner: Murder, two counts of unlawfully firing a gun in a public place in unrelated incidents and one count of illegal possession of ammunition.
Before the session began, Pistorius hugged his brother Carl, who was seated in a wheelchair because of injuries suffered in a recent car crash.
The parents of Steenkamp were also in the packed gallery. Other members of Pistorius' family, including his father Henke, sat behind him.
If Pistorius is convicted on any charge, the case will likely be postponed until a later sentencing hearing.
There were many journalists at the courthouse, where the sensational trial has unfolded over the last six months.
