TULSA, Oklahoma - A Tulsa mother serving a life sentence for her baby's murder could be spending her last night in jail. Michelle Murphy has been behind bars for 20 years, but new evidence could set her free.

Murphy was moved to the Tulsa County jail when her attorneys challenged her conviction. She could walk out of jail, as soon as Friday, after the District Attorney announced new DNA evidence that wasn't available at Murphy's trial.

Murphy was just 17 years old when she was cuffed and eventually convicted of slitting her 3-month-old son's throat.

"It's a terrible tragedy, it's an incredible tragedy," Richard O'Carroll, Murphy's attorney.

He said the tragedy is two-fold. Not only has she lost her son, she's also lost 20 years of her life, sitting in prison for a crime, O'Carroll says his client didn't commit.

"This is just the beginning of the exposure of the malfeasance in this case," he said.

O'Carroll and his wife and law partner, Sharisse, took on Murphy's case four years ago. He said, plain and simple, Murphy did not receive a fair trial.

"Evidence was withheld, it wasn't looked for diligently and people cheated," O'Carroll said. "We have enough factual evidence, just the regular, old kind of evidence to exonerate her, in my opinion."

New DNA tests cast doubt on evidence presented at Murphy's trial.

According to court documents, the state originally said a blood sample found at the crime scene did not belong to the baby. Turns out, it did.

District Attorney Tim Harris said if that evidence had presented, it could have affected the verdict. Harris asked for Murphy's murder conviction and sentence to be vacated.

"It's a step and it's not enough, not even close to enough," O'Carroll said. "But, we are not done and we will not rest until she is exonerated."

O'Carroll said there was a second blood sample found at the scene. He said that blood doesn't match Murphy's either.

O'Carroll claims it belonged to the prosecutor's star witness, William Lee, who committed suicide before the case went to trial.

He said there's a hearing Friday morning, where he hopes the judge will set Murphy's bond; she could be out later on Friday.

A re-trail would be the next step, so she'll be free once released, unless she's convicted a second time.