Complex sentence: Once in safety, Miranda reveals that she had witnessed the murder Joyce claimed she had seen; more precisely, she saw Garfield and Rowena drag Olga's body through the quarry garden and only later realized she had witnessed a murder.
Split into simpler sentences: Once in safety, Miranda reveals that she had witnessed the murder Joyce claimed she had seen. She saw Garfield and Rowena drag Olga's body through the quarry garden and only later realized she had witnessed a murder.