(ABC News) -- A teenage friend of Trayvon Martin was forced to admit today in the George Zimmerman murder trial that she did not write a letter that was sent to Martin's mother describing what she allegedly heard on a phone call with Martin moments before he was shot.
In a painfully embarrassing moment, Rachel Jeantel was asked to read the letter out loud in court.
"Are you able to read that at all?" defense attorney Don West asked.
Jeantel, head bowed, eyes averted whispered into the court microphone, "Some but not all. I don't read cursive."
It sent a hush through the packed courtroom.
Jeantel, 19, was unable to read any of the letter save for her name.
The testimony was an attempt to raise questions about veracity of Jeantel's testimony, who is a key prosecution witness in the racially charged case.
Zimmerman, 29, is on trial in the Florida courtroom for second degree murder in Martin's Feb. 26, 2012 death.
Jeantel was subdued on the stand today, in contrast to her openly hostile demeanor towards Zimmerman's lawyers on Wednesday. Her behavior was so different that defense lawyer Don West asked Jeantel, "You seem so different from yesterday. I'm just checking, did someone talk to last night about your demeanor in court?"
Jeantel replied that she had gotten some sleep.
Rachel Jeantel was the last person to speak on the phone with Martin moments before he was shot to death by Zimmerman on Feb. 26, 2012.
During cross examination today, Jeantel also testified that she when she was interviewed under oath on April 2 by prosecutor Bernie de la Rionda she was sitting next to Trayvon Martin's mother and that influenced what she told the prosecutor.
"You certainly didn't want to say anything that you thought would hurt her feelings or make her grieve even worse," asked West.
"Yes sir," she responded.
"So because of that you were sensitive to (Martin's mother) Mrs. Fulton's feelings when you answered Mr. De la Rionda questions."
"Yes sir," she replied.
"And that's why you cleaned up some of the language that Trayvon Martin used?" West asked.
"Yes sir," she responded.
During nearly two hours of cross examination Wednesday in which he tried to raise questions about her version of events and accused her of telling several lies under oath, including about her whereabouts during Martin's wake.
"Under oath, you created a lie and said you went to the hospital?" asked West.
"Yes," responded Jeantel. She said she lied because she didn't want to see the body.
Jeantel became increasingly agitated and scoffed when West told her that she would have to continue testifying.
She is seen as a critical witness to the prosecution because she is the only person able to say that Martin claimed that he noticed a strange man following him and that he was scared. Jeantel said Martin described the stranger as a "creepy ass cracker."
Jeantel said Martin, 17, was walking home during halftime of the NBA All-Star Game when he became unnerved because he was being followed.
"He told me the man kept following him," Jeantel said.
Jeantel said she told Martin to run, but that he responded that he was almost home.
"I say, 'Trayvon,' and then he said, 'Why are you following me for?'" Jeantel testified. "And then I heard a hard-breathing man come say, 'What you doing around here?' ... And then I was calling, 'Trayvon, Trayvon.' And then I started to hear a little bit of Trayvon saying, 'Get off, get off.'"
At times during her early testimony with the prosecution, Jeantel dabbed away tears.
During cross-examination, defense attorney Don West tried to dig into the chain of events preceding Martin's death. West asked why Jeantel didn't call law enforcement after the phone died.
"I thought he was going to be OK because he was right by his daddy's house, but his daddy was not home," Jeantel said as Martin's father cried in court.
Tracey Martin eventually reached out to Jeantel after looking at his son's phone log, Jeantel said. She added that she expected law enforcement to reach out to her, but none did, apparently, until the Florida Department of Law Enforcement contacted her much later.
Zimmerman, said he was defending himself from Martin after the unarmed teenager allegedly confronted him, knocked him down and banged his head of the sidewalk. Prosecutors allege that the former neighborhood watch captain profiled and followed the teenager before killing him.