When detectives interviewed the mother, she recounted how she was heading to bed early Tuesday morning when she saw her boyfriend lying on top of her daughter without any clothes on.
In a fit of rage, according to the police report, she grabbed her pocketknife and lunged at him.
The couple wrestled over the knife, and at one point the man allegedly grabbed his girlfriend by the throat and hurled her against the wall.
Both the mother and daughter sustained cuts to their hands as a result of the fight.
The 12-year-old girl told police her mother's boyfriend fondled her under her clothes, removed her pants and stripped off his own clothes.
He then told her, "this is what it is like in the real world when you have a boyfriend," before sexually assaulting her, according to police.
The victim of the stabbing offered a different version of events, suggesting that his girlfriend may have attacked him out of jealousy, because she thought her young daughter has developed feelings for him.