Oscar Pistorius's girlfriend Reeva Steenkamp told the athlete that she was sometimes scared of him in a text message sent less than three weeks before he shot her dead.

"I'm scared of you sometimes and how you snap at me and how you react to me," Ms Steenkamp said via messaging service WhatsApp after the athlete apparently created a scene thinking that she had flirted with another man.

As the trial entered its fourth week, police mobile phone expert Francois Moller read out several exchanges between the couple.

He said 90% of the messages were loving, but in one long message Ms Steenkamp said the athlete had been picking on her "incessantly".

"We are living in a double standard relationship where u can be mad about how i feel with stuff when u are very quick to act cold and offish when you're unhappy," Ms Steenkamp said on 27 January last year.

"You make me happy 90% of the time and I think we are amazing together, but I'm not some other b***h not trying to kill your vibe," she added.

"Why try anymore? I get snapped at and get told my accents and voice is annoying," she continued.

Police downloaded call records and data from two iPhones, two Blackberries and two iPads found at Mr Pistorius's home after he shot dead the 29-year-old model on 14 February last year.

The athlete denies the premeditated murder charge, saying the couple was in a loving relationship and that he fired four shots through a locked toilet door after he mistook Ms Steenkamp for an intruder.

There was also further testimony on gunshots and a woman's screams on the night the Olympic and Paralympic shot dead his girlfriend.

Anette Stipp, a neighbour, said she heard shots, then a woman screaming, then more gunshots in the early hours of the morning on Valentine's Day last year.

"I heard three, which sounded to me like gunshots," said Ms Stipp.

"It was moments after the shots I heard a lady screaming. Terrified, terrified screaming," she said.

Prosecutors said they will finish presenting their case of premeditated murder against Mr Pistorius early this week, when the defence will start calling their witnesses.

The trial is already running over schedule and may now last until 16 May, with a short court recess in April.

Ms Stipp's evidence contradicts the 27-year-old sprinting star's account that he shot Ms Steenkamp after mistaking her for an intruder.

The defence has argued that the shots that killed Ms Steenkamp came too fast for her to scream out and alert her boyfriend that it was her in the toilet.

The defence has also said the screaming was not Ms Steenkamp, but actually Mr Pistorius who screams "like a woman" when he is anxious.