Oscar Pistorius was allegedly surfing porn websites on his mobile phone the night he shot model girlfriend Reeva Steenkamp in his Pretoria home.
A leaked document believed to be part of the court investigation reportedly alleges the athlete was surfing pornographic material on his mobile while Steenkamp was in the house on Valentine's Day in direct contrast to "a loving couple spending their time together".
The new allegation comes only days after leaked documents filed by prosecutors in South Africa claimed Pistorius told concerned security outside his home that everything was "fine" after the shooting last year.
Prosecution documents also revealed Pistorius was "most likely on his stumps" and fired at the bathroom door where Steenkamp was shot dead from a greater distance than the 60cm initially reported by police.
These contradict earlier claims that Pistorius, 27, took the time to put on his prosthetic legs, suggesting that he did not panic about the prospect of an intruder breaking into his gated community villa.
The athlete said he shot her in a case of mistaken identity.
Prosecutors said he intentionally shot and killed Steenkamp , 29, through the locked door of his bathroom following a domestic dispute. If convicted of premeditated murder, he could face life imprisonment with a minimum of 25 years before parole.
Earlier this month, Pistorius broke his silence to reveal he is "consumed" with "pain and sadness" in a statement released to mark the first anniversary of Steenkamp's death.
He said: "No words can adequately capture my feelings about the devastating accident that has caused such heartache for everyone who truly loved - and continues to love Reeva.
"The pain and sadness - especially for Reeva's parents, family and friends consumes me with sorrow. The loss of Reeva and the complete trauma of that day, I will carry with me for the rest of my life."
Steenkamp's parents, June and Barry, said the family is looking for closure ahead of the trial and confirmed the model's mother will attend the trial in Pretoria next Monday.
In a statement, they said: "All we are looking for is closure and to know that our daughter did not suffer on that tragic Valentine's Day."
More than 100 witnesses are expected to appear in court; including Pistorius' sister, Aimee, former girlfriends Melissa Rom and Samantha Taylor, residents of gated community Silver Woods in Pretoria and a team of medical, ballistic and forensic experts.
The trial is due to start on 3 March.