By LIEZL THOM

PRETORIA, South Africa - Oscar Pistorius has been contradicted several times during his trial for shooting his girlfriend Reeva Steenkamp as the prosecution has clearly tried to cast doubt on his insistence that he killed Steenkamp when he mistook her for a burglar.

Pistorius has accused his ex-girlfriend Samantha Taylor of lying when she testified, accused the media of printing lies about him and the police of moving around key pieces of evidence.

Prosecutor Gerrie Nel today told Pistorius his version of what happened the night he killed Steenkamp was "so improbable that nobody would think it is reasonably true."

Since Pistorius is testifying in his own defense, his credibility is key to avoiding prison. If convicted of murder, the Blade Runner could face at least 25 years in prison.

Among the contradictions that Pistorius will have to deal with so far:

• One of the charges against Pistorius is a weapons charge for allegedly firing a gun through the sunroof of a car. Pistorius denied today that he ever fired through a car roof. But Taylor and Pistorius' friend Danny Fresco testified last month that Pistorius allegedly fired a shot through the open sunroof of a car in September 2012 after an altercation with a police officer. Pistorius claims they both lied. "That story was fabricated… it never happened," Pistorius told the court.

• Pistorius is also accused of a second weapons charge because a gun he was handling in a restaurant discharged. Pistorius said today he did not have his finger on the trigger and that he did not fire the gun. He also claims that Fresco volunteered to take responsibility for the gun going off.

Fresco, however, told the court that the gun went off as he handed it to Pistorius under a table and that Pistorius asked Fresco to say it was his fault so Pistorius could avoid bad press.

• Pistorius told the court that Steenkamp was not afraid of him, but text messages Steenkamp sent to Pistorius were read in court in which Steenkamp told Pistorius "I'm scared of you sometimes and how you snap at me," and "i am the girl who let go with u even when i was scared out of my mind to."

Reeva Steenkamp Duif du Toit/Gallo Images/Getty Images

• Pistorius told the court that he was so terrified when he allegedly thought there was an intruder in the bathroom that when he heard a noise he involuntarily fired four times in rapid succession. Prosecutor Gerrie Nel noted in cross examination that Pistorius' lawyer Barry Roux told the court that there were two "double taps," two quick shots fired and then two more quick shots fire. Pistorius replied that he later corrected his attorney.

• Outside of court, Taylor tweeted this, "Last lies you get to tell. You better make it worth your while." The tweet came after Pistorius testified that Taylor had tried to get back with him after they broke up, that she was with someone when he was overseas and that someone set up a fake Twitter account to pick on Steenkamp. She later deleted the tweet.

• Pistorius has accused police of moving around objects in his bedroom during their investigation. Nel asked why a policeman would move the items and asked if there was a conspiracy against him, to which Pistorius replied: "I'm not sure, My Lady."

Esa Alexander/The Times/Gallo Images/Getty Images