Scott Peterson is finally speaking from behind bars … 20 years after he was convicted of killing his wife, Laci Peterson, and their unborn child.

In the new “Face to Face with Scott Peterson” Peacock doc, the convicted murderer maintains his innocence … and sticks to his guns about his long-standing theory his pregnant wife Laci was abducted by strangers who were burglarizing a neighboring home.

Scott spoke on camera for the first time from California’s Mule Creek State Prison … detailing his assertions about Laci’s death with interviewer Shareen Anderson for the 3-part doc, which digs into alternate theories about Laci’s death.

Peterson’s 2002 case has stayed in the limelight over the years … and in 2021, his death sentence was knocked down to life without parole … after the California Supreme Court found some jurors were improperly dismissed.

Scott’s case was picked up by the L.A. Innocence Project earlier this year … and could potentially lead to a new trial — something Mark Geragos, Peterson’s lawyer from his 2004 trial, told us he couldn’t be happier about.

Quick refresher … Laci was 8 months pregnant with Peterson’s baby when she disappeared on Christmas Eve ’02. Her body was discovered in the San Francisco Bay months later.

Peterson became the prime suspect after cops found out he was cheating with a massage therapist — and he was arrested for murder in April 2003.