Jurors in George Zimmerman's second-degree murder trial will hear more today from the friend who was on the phone with Trayvon Martin right before he was shot. 19-year-old Rachel Jeantel testified yesterday that when Martin said he was being followed, she told him to run.

Jeantel is a key state witness. She said Martin told her Zimmerman was watching him, so he ran. Jeantel then said Martin spotted Zimmerman again near the townhome where he was staying with his father."He said, Why are you following me for? And I heard a hard-breathed man come and say, 'Whatcha doing around here'", Jeantel testified.

Jeantel said she heard Martin say, "Get off!", and the phone went dead.

Earlier another witness - Jane Surdyka - described hearing two voices, one high pitched, the other aggressive and dominant.

"I truly believe, especially the second yell for help that was like a yelp. It was excruciating", said Surdyka. "I really felt it was a boy's voice."

The cries for help are at the center of the case, but there's no consensus on whose voice it was.

Prosecutors say Zimmerman profiled, followed and murdered Martin. But Zimmerman says Martin attacked him, forcing him to fire in self-defense.