A 9-1/2 minute argument between girlfriends escalated dramatically on the 69th Street Red Line platform as they stood "chest-to-chest" and one of them held out a gun and opened fire, a prosecutor said Friday.Tiara Lee-Roberts, 28, fatally shot her on-again, off-again girlfriend of nearly a year Tues day evening before turning herself in to police hours later, Cook County Assistant State's Attorney Todd Kleist said in court Friday.Lee-Roberts was charged with first-degree murder, police said. The victim, identified by the Cook County medical examiner's office as 30-year-old Kamari McMillen, died from a gunshot wound to her neck.William Wolf, an attorney for Lee-Roberts, said she accidentally fired her weapon as she was pushed by McMillen. Wolf said McMillen "completely initiated" the confrontation.But the prosecutor said, "You don't accidentally place a firearm to someone's neck and fire it... This was first-degree murder."Judge Shauna Boliker agreed that the shooting was not accidental and ordered Lee-Roberts detained pending trial."This was a vicious response to a verbal altercation," the judge said.The evening began at a dinner at McMillen's family's home, Kleist said. The women left the home separately after dinner concluded, but met each other again on the CTA platform around 9:35 p.m., Kleist said. That's when McMillen confronted Lee-Roberts on the platform and the two began arguing, he said.McMillen escalated the argument into a physical fight when she swung her arm, Kleist said. It is unclear in surveillance video, which captured most of the fight and shooting, if she made contact with Lee-Roberts, Kleist said.McMillen then picks up something off the ground and swings it, he said. The video shows allegedly Lee-Roberts drop something to the ground. McMillen picks it up, rips it apart and throws it on the tracks, he said.As Lee-Roberts walks away, McMillen approaches and punches her in the back of the head, Kleist said.The video shows Lee-Roberts walk away and pull out a semi-automatic handgun, pointing it at her partner, Kleist said. McMillen approaches and, "face-to-face, chest-to-chest," Lee-Roberts puts her finger on the trigger, Kleist said.Lee-Roberts then strikes the woman's neck with the gun, Kleist said. McMillen pushes back, after which Lee-Roberts fires the gun, striking her neck, then runs away, Kleist said. She turned herself into police about two hours later, he said.Lee-Roberts attorney said one detail is contradicted in a police report. Wolf said the report says Lee-Roberts pushed back as the gun went off — "not that the defendant pushes back and, a distance away, she shoots her," he said."She said this was an accident," Wolf said.Contributing: Kade Heather ...read more read less