A neighbor of Oscar Pistorius described hearing "blood-curdling" screams the night the South African athlete shot and killed his girlfriend, Reeva Steenkamp.
Pistorius' long-awaited murder trial got under way Monday with the double amputee athlete pleading not guilty to all charges against him stemming from the Feb. 14, 2013, shooting death of Steenkamp.
Pistorius, 27, responded, "Not guilty, my lady," to every charge before Judge Thokozile Masipa.
He looked calmer during this court appearance than he did a year ago during a tear-soaked, trembling appearance just days after he shot his model girlfriend dead at his Pretoria home.
He doesn't deny shooting Steenkamp. The trial is about his intent. Pistorius claims he mistook his girlfriend of three months for an intruder and did not mean to kill her when he shot four times through a locked bathroom door.
The prosecution says they will prove premeditated murder.
The state called the first of 107 witnesses, Michelle Burger, a neighbor of Pistorius who described what she heard on the evening of the shooting.
Burger, whose home is 177 meters from Pistorius', said she was awakened by a woman's "blood-curdling" screams, followed by a man's cries for help. She then says she heard four gunshots, while the woman continued screaming.
"She was very scared...her shouts, her screams were petrifying," Burger said. "Before the gunshots, moments before the gunshots, I sat in the bed and it's the most helpless feeling I've ever had in my life. I anticipated something was going to happen, because of the climax of her shouts, I knew something terrible was happening in that house."
Burger testified she and her husband thought they were hearing a violent house break-in and called security. She said it only occurred to her later, upon seeing the news of the shooting at Pistorius' home, that that is what she had heard.
The athlete's defense lawyer, Barry Roux, suggested Burger instead heard the sound of Pistorius breaking down the bathroom door with a cricket bat, consistent with his client's account of events.
But Burger steadfastly stuck to her account.
The families of Pistorius and Steenkamp were also in court Monday, seated a few meters apart on opposite ends of a long bench.
Legal experts predict the trial could take months and, given today's lengthy witness appearance, that appears likely.
Pistorius shot to fame for being the first double amputee to compete in the Olympics in 2012. He also has won medals at the Paralympic Games.
Parts of the trial are being televised live. A South African station has launched a 24-hour channel dedicated solely to the case.