(CNN)-- The state's chief witness in the Trayvon Martin murder case lied under oath, prosecutors say.
The young woman who says she was on the phone with Martin when he encountered George Zimmerman lied about her whereabouts at another time, the prosecution told a judge Tuesday.
The woman, whose name has not been released, had told prosecutors that she was in the hospital on the day of Martin's funeral. The defense then sought her medical records.
In court on Tuesday, the state said the woman, known as Civilian Witness 8, was not in the hospital, so there are no such records to be turned over.
Prosecutors did not immediately respond to a question Wednesday from CNN about the witness's credibility and how this may affect the case.
Questions have long surrounded the woman. Martin family attorney Benjamin Crump first played an audio recording of the woman a year ago at a news conference. The recording seemed to have very poor quality.
Police said that as of that point they had not interviewed her.
Crump said the witness was 16 years old. But prosecutors have since said she was already 18 -- legally an adult -- on the night of the killing, February 26, 2012, in Sanford, Florida.
Martin, 17, was walking to the house of his father's fiancee after a trip to a nearby convenience store.
Zimmerman, a neighborhood watch volunteer, has acknowledged shooting Martin.
Crump has accused Zimmerman of killing Martin "in cold blood."
Zimmerman says he acted in self-defense.