If the evidence points to the truth, the tapes will become inadmissible in a court of law.
The LA County Sheriff's Department would have to authenticate the tapes before they can be used in any court situation - which requires they be sent to the DA's office and could take an indefinite time to complete. According to the website:
As we first reported, Mel's lawyers will be presenting evidence to the Sheriff's Department and we're told among the evidence they will present -- that the tapes have been altered. We're told Mel's lawyers will present "concrete forensic evidence" of tampering with the tapes, including editing.The site also reveals that Gibson denies ever hitting Oksana. [Via TMZ]
Oksana's attorneys tell TMZ, "We are not aware of any presentation Gibson's lawyers are making, but we are not surprised they would make such unfounded claims."