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The star prosecution witness took the stand in a Florida courtroom for a second day Thursday as George Zimmerman’s attorneys tried to demonstrate that her story about hearing the prelude to the defendant's fatal confrontation with Trayvon Martin has changed over the course of the last year.

Defense attorney Don West grilled Rachel Jeantel about a letter she had a friend write for Martin's parents in the weeks after the February, 2012 incident, describing the phone conversation she had with Martin as he walked from a convenience store in Sanford, Fla., back to his father’s fiancee’s home in a gated community. West pressed her on what he indicated were inconsistencies between the letter and Jeantel's subsequent depositions and testimony - in particular her recent revelation that Martin told her he was being  followed by a "creepy-ass cracker."

"Why wasn't 'creepy-ass cracker' in prior interviews?" asked West, one of the attorneys for Zimmerman, who is facing a charge of second-degree murder.

"Nobody asked me," replied Jeantel, who said she can't read cursive, which the letter is written in.

The letter, in which Martin's name is spelled wrong, describes how Jeantel was speaking by cell phone with the 17-year-old Martin as he cut through a subdivision on his way to the home where he was staying. Jeantel has said she had the letter written for Martin's parents to give her account, but that she never intended for it to be made public.

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"He started walking then noticed someone was following him," read the letter. "Then he decided to find a shortcut cause the man wouldn't follow him. Then he said the man didn't follow him again. Then he looked back and saw the man again. The man started getting closer. Then Trevon turned around and said Why are you following me!! Then I heard him fall. Then the phone hung up. I called back and got no response. In my mind I thought it was just a fight. Then I found out this tragic story. Thank you."

But on Wednesday, Jeantel, 19, told jurors Martin said he was being followed by “a creepy-ass cracker” just before the fatal confrontation with Zimmerman, a neighborhood watch volunteer who is charged with second-degree murder in Martin’s death. She said she warned Martin to walk away, saying "it might be a rapist."

Martin, she said, told her he was going to try to "lose him" and get to the home. But Jeantel said as she remained on the phone with Martin, the man who was allegedly following him reappeared, prompting the confrontation, of which she heard the initial moments.

West questioned what he portrayed as a change in the Jeantel's characterization of the confrontation, which is critical because much of Zimmerman's defense rests on showing that he acted in self-defense, while prosecutors say it was Zimmerman who provoked the incident by aggressively stalking Martin. Jeantel has consistently said she heard Martin ask Zimmerman why he was following him. But in an earlier account, she said Zimmerman replied, "What are you talking about?" while in the latest testimony, she claimed Zimmerman replied "What are you doing around here?"

After the two had words, Jeantel testified she heard Martin's phone headset fall and then Martin say "Get off!" The phone went dead shortly after and Jeantel says she didn’t speak to Martin again.

West asked Jeantel why she did not tell Martin's family or their lawyer, Benjamin Crump, about Martin yelling "Get off!" Jeantel replied, "because Crump is not law enforcement."

Jeantel also testified she heard something that sounded like a "bump" before the phone went dead.

When asked by West if she had previously told investigators that she heard what sounded like somebody being hit at the end of her call with Martin, Jeantel said, "Trayvon got hit."

"You don't know that? Do you? You don't know that Trayvon got hit," West answered angrily. "You don't know that Trayvon didn't at that moment take his fists and drive them into George Zimmerman's face."

Jeantel's testimony is key to the prosecution's argument that Zimmerman was the aggressor in the fatal confrontation. West tried repeatedly to chip away at Jeantel's testimony, including in one heated exchange over whether Martin would have told Jeantel if he had decided to start a fight with Zimmerman.

"Of course, you don't know if he (Martin) was telling the truth or not," West asked Jeantel.

"Why he need to lie about that sir?" replied Jeantel.

"Maybe if he decided to assault George Zimmerman he didn't want you to know about it?" answered West.

"That's real retarded, sir," Jeantel said. "When you don't know the person, why risk it? Trayvon didn't know him."

Later in the morning, West accused Jeantel of not calling police after she lost contact with Martin because she thought it was a fight he had provoked.

"That's why you weren't worried. That's why you didn't do anything because Trayvon Martin started the fight and you knew that," West said.

"No sir!" Jeantel said. "I don't know what you're talking about."

SPECIAL COVERAGE: ZIMMERMAN TRIAL

Jeantel has come under fire in the past for lying about her age -- claiming to be 16 in order, she said, to avoid getting dragged into the case. She also admitted lying about her reasons for not attending Martin’s funeral, saying she was in the hospital. In her testimony, she said she didn’t go because she felt guilty.

Jeantel's testimony was more subdued on Thursday, and West took note of her calmer demeanor. She answered many of West's questions by repeating "yes, sir," almost in a whisper.

"You feeling OK today? You seem different than yesterday," West said.

"I got some sleep," she answered.

After Jeantel left the witness stand, a mobile phone manager testified about Martin's cell phone records and a former neighbor of Zimmerman testified she heard yelps for help outside her townhome on the night Martin was shot. Jenna Lauer said she couldn't tell who was screaming.

"They were being hurt," Lauer said, describing the person screaming.

Before court recessed for the day, defense attorney Mark O'Mara asked another former neighbor to recreate for jurors how she reacted when she heard what turned out to be a gunshot and ran out of her town-house to see what was going on. The request had Selma Mora in the unusual position of standing up from the witness stand and pretending to be in her kitchen in front of the judge's bench.

Zimmerman, 29, has said he opened fire only after the teenager jumped him and began slamming his head against the concrete sidewalk. Zimmerman identifies himself as Hispanic and has denied that his confrontation with the black teenager had anything to do with race, as Martin's family and its supporters have claimed.

Zimmerman has pleaded not guilty, claiming self-defense. He could face life in prison if convicted.

Fox News' Serafin Gomez and The Associated Press contributed to this report.