Proceedings began late Wednesday morning and the first witness called was Michael Yancey, who lives near the Mount Vernon school, which was the scene of the crime.
Yancey's testimony came on the second day of the trial of Rodolfo Godinez
The trial is focused on what happened on August 4, 2007 when Dashon Harvey, Iofemi Hightower and Terrance Aeriel were shot execution style.
Prosecutors say they were killed as part of a gang initiation.
Yancey testified hearing a woman's voice that night.
"It said 'Don't do that. Why you want to do that,'" Yancy testified. 'It was like begging for mercy.'"
Yancey went on to say that he heard the woman's voice again, asking the same question and sounding angry.
Soon after, he heard a woman's scream and four gunshots.
Prosecutors also showed the photos during testimony by a paramedic who responded to the scene.
Witness Derron Brice and his partner were the first paramedics to arrive at the Mount Vernon playground after reports of shots fired. Looking at enlarged photographs today, he described the scene they walked upon.
"What do you recognize in that photograph?" asked prosecutor Thomas McTigue.
"The 3 dead bodies near the stairs," Brice replied.
Brice said they could tell that Harvey, Hightower and Aerial were dead, so they turned their attention to the lone survivor found in another area of the playground.
"I thought it was a lifeless dead body, but she had shallow breathing. I'd assumed she was dead," Brice testified.
But then, Brice said, she began to speak.
"She was making utterances like get her brother and her friends. I was focused on saving her life," he said.
Some family members of the victims closed their eyes, as graphic pictures of the executions were shown. One mother of a victim walked out.
Suspect and MS-13 gang member Roldolfo Godinez is the first of 6 defendants to go to trial for the August 2007 murders. He barely made movement during testimony today.
A key witness, the 19 year old woman who survived the attack, is now expected to testify on Thursday, prosecutors said.
The prosecution says the woman was sexually assaulted, cut with a knife and shot in the head when she ran screaming.