Convicted Manson family killer Leslie Van Houten contends there is missing evidence that could set her free.

Van Houten, 67, contends prosecutors are hiding a recording that could lead to her release at her next parole hearing, according to TMZ.

Her lawyer, Richard Pfeiffer, has reportedly filed court documents to ban prosecutors from appearing at her upcoming hearing because they will not release a tape featuring Charles Manson's trusted pal Tex Watson.

Van Houten has said that the tapes will prove her claims that she was under Manson's spell at the time of the killings.

She maintains that she was under Manson's control at the time of the murders and now, after 39 years in prison, she is no longer under his spell and no longer a threat to society.

The prosecution reportedly fired back and said that the tapes feature nothing but, “rambling musings about LSD, secret worlds beneath Death Valley and bizarre racial theories.”

Van Houten, who was convicted of murder in 1978, has served 39 years of a life sentence in the killing of Leno and Rosemary LaBianca back in August of 1969.

Her next parole hearing is scheduled for September.