According to People mag, which has seen an early release of the new Peacock doc, "Casey Anthony: Where the Truth Lies" ... Casey spills her guts on camera, accusing George Anthony of staging Caylee's death to make it seem like it was Casey's fault, all in an alleged effort to cover up what Casey claims might've been sexual abuse at his hands.

In the documentary, Casey reportedly claims she fell asleep with 2-year-old Caylee on top of her on June 16, 2008 ... only to be awoken by her dad in the middle of the night with Caylee missing and George asking where she was. Casey says it didn't make sense for Caylee to be gone, because she says the kid would never leave a room without telling her.

She claims George eventually presented her with Caylee's dead body, which was soaking wet and cold and allegedly told Casey she had caused this. Casey then claims he took Caylee's body and disappeared ... again, according to People's review.

Casey's theory, all these years later, is George allegedly smothered Caylee with a pillow to knock her out, and drowned her in their above-ground pool. Casey says she doesn't believe Caylee would be able to get in there on her own ... as she says there was no ladder.

Casey had already accused George of sexually abusing her when she was a child, and of disposing of Caylee's body -- claims he vehemently denied in court -- but now she's taking it a step further by suggesting he planned the whole thing ... Caylee's death included.

People reports Casey says she believes her father had moved on to her kid, and wanted to hide it by getting rid of Caylee and framing Casey. As for why it took Casey so long to report her missing ... she says she was under the delusion Caylee was still alive, apparently in denial she'd died, and allegedly following her dad's instructions in the aftermath.

Of course, you know the jury acquitted Casey of murder, manslaughter and child abuse. She was found guilty of lying to cops, but that's it.