PRETORIA, South Africa – Testimony in the murder trial of Oscar Pistorius is focusing on the screams that neighbours heard on the night that the athlete killed girlfriend Reeva Steenkamp.

Chief prosecutor Gerrie Nel on Tuesday questioned an acoustics expert who had been called by the defence team as part of its effort to suggest some neighbours who testified they heard the screams of a woman were wrong, and that they actually heard the high-pitched screams of the double-amputee runner.

Pistorius fatally shot Steenkamp through a closed toilet door in his home in the early hours of Feb. 14, 2013.

He has testified that he fired in the mistaken belief there was a dangerous intruder in his home. The prosecution has alleged that Pistorius killed Steenkamp after a Valentine’s Day argument.