What I think happened

Amanda, Rudy, and Raf are hanging out and doing drugs in the kitchen. Meredith comes home.

Conflict between Amanda and Meredith. Tense words exchanged about clothes or money or both. Meredith heads back to her room.

Amanda follows her. Raf follows Amanda. Raf closes the door behind him once in Meredith's room.

Amanda and Raf sexually abuse and taunt Meredith on her bed. This is where most of the physical conflict takes place.

Rudy is still in the kitchen. At some point he uses the toilet and leaves the poo. Once he returns to the kitchen, he hears Meredith scream.

The conflict has escalated in the bedroom, but they've moved from the bed to a different location.

Rudy runs in and tries to save Meredith with towels. He robs her before freaking out about the scene and fleeing the house.

Amanda and Raf wash Meredith's sheets. They penetrate Meredith with a beer bottle or other object that Rudy was holding, to leave a traces of his DNA. They use a black light to clean the rest of the room, especially the area around the bed, of their DNA.

Rudy doesn't tell the cops that he was hanging out with Amanda / Raf to align himself with Meredith rather than the killers.