Update at 12:36 p.m. ET: "What Zimmerman said is completely contradicted by the phone log," says Crump.
He also says voice experts are running through the 911 tapes to see who was yelling for help.
"The dots have all been connected, arrest George Zimmerman for the killing of Trayvon Martin in cold blood today," the lawyer says.
Update at 12:32 p.m. ET: "This claim that Trayvon Martin was the aggressor is preposterous and cannot be allowed to stand," Crump says.
"That is what Zimmerman wants you to believe so he can justifiy killing this kid in cold blood," he says.
Update at 12:27 p.m. ET: Crump says the two teens had been talking most of the day and that the last call began at 7:12 p.m. He said the police, who had been called by Zimmerman, arrived on the scene at 7:17 p.m.
A 911 call from a neighbor includes someone shouting "help" and the sound of a gunshot. The girl did not hear this part of the confrontation, says Crump, because the phone had been knocked out.
But Crump says three witnesses have come forward to say that it was Trayvon's voice yelling "help" just before the shooting.
Update at 12:23 p.m. ET: Crump, relaying the girl's description of the conversation with Trayvon as the confrontation heats up, says, "She hears other voice, 'what are you doing around here?' Trayvon says, 'Why are you following me?'" At that point, according to the girl, Travyon is pushed and his voice changes.
"She hears the altercation, suddenly, someone just hit the phone, because that's the last she hears," Crump says.
Update at 12:18 p.m. ET: According to the girl, Trayvon says, "I think I lost him" then moments later says, "He is right behind me again. I'm not going to run, I'm going to walk fast."
Update at 12: 17 p.m. ET: Crump: "She tells him, 'baby, be careful, just run home.'"
Update at 12:15 p.m. ET: The lawyer, who took an affidavit from the girl, quotes her as saying that Trayvon was walking home from the store Feb. 26 and had temporarily taken refuge from the rain. He then began walking again, when he tells her, according to Crump, "I think this dude is following me."
Update at 12:10 p.m. ET: Crump, the lawyer for the Martin family, says Trayvon had been on the phone with his girlfriend most of the day, including his walk to a 7-11 and back, as the confrontation unfolded.
He says the unidentified girl was "traumatized" by what she heard and had to be hospitalized.
"She couldn't even go to his wake, she was so sick. She spent the night in the hospital," Crump says. "She is traumatized beyond anything you could imagine."
Update at 12:08 p.m. ET: Crump says Trayvon was speaking with a 16-year-old girlfriend who was in Miami. He says the last called lasted for four minutes during his confrontation with George Zimmerman, a white Hispanic and the neighborhood watch volunteer who killed the boy in what he claimed was self-defense.
Update at 12:06 p.m. ET: Benjamin Crump, attorney for the Martin family, says the teenager's family "does not trust the Sanford police department in anything they do with the investigation."
Update at 11:21 a.m. ET: The Seminole County grand jury will take up the case April 10, according to a statement by State Attorney Norm Wolfinger.
He said that his office, with the help of the Florida Department of Law Enforcement, is reviewing and collecting evidence in the case.
"I respectfully request that the public remain patient as this process moves forward," the statement said.
