By Laura Cole

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EL DORADO COUNTY (CBS13) — El Dorado County teen murder suspect Tylar Witt is set to take the stand tomorrow in the killing of her mother Joann Witt.

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Tylar and one-time boyfriend Steven Colver are both facing charges in the killing, and legal experts say her testimony could make or break the prosecution’s case.

When Tylar takes the stand on Wednesday her words and her demeanor will be scrutinized by the jury, which are key components that will make or break the prosecution’s case

“I think her testimony is absolutely critical,” said defense attorney Jennifer Mouzis.

But Tylar Witt isn’t exactly the ideal witness. She’s taken a plea deal for her testimony against her Steven Colver.

“In some ways I think it will be hard for a jury to believe she has been given a plea bargain and that’s going to be a motive, according to the defense, for her to lie,” said Mouzis.

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Prosecutors allege that Colver killed Witt’s mother, Joanne, in 2009 after she filed a statutory rape complaint against him involving her daughter. But the defense claims it was Witt who killed her mother, and that Colver was only covering for his then-girlfriend to protect her.

“In a way the whole case does rest on her shoulders,” said Mouzis. “What the prosecution needs her to do is tell the truth. And the truth is a very compelling thing when you see it on the stand.”

But will it be enough? Witt will have to answer hundreds, if not thousands of questions especially under intense cross examination. And the picture the defense will paint will make her out to be an evil manipulator.

And in this classic case of he-said, she-said, Colver will have to take the stand if he wants the jury to believe that he lied to protect his girlfriend.

“They really promised the jury a lot. In this case they promised to show that Stephen Colver is a nice kid, that he had no motive to commit this crime, that he was trying to help Tylar Witt and that he came in after the murder,” said Mouzis.

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Witt’s testimony was delayed last week after new DNA evidence came to light. Attorneys are arguing over whether it can be used at trial. In exchange for Witt’s testimony she will receive 15 years to life instead of 25 years to life.