Complex sentence: According to the girl Curtis then asked her if her parents were how, she said they were not, and he attacked her and attempted to rape her but, unbeknownst to Curtis, her brother had called the police who arrived on the scene.
Split into simpler sentences: According to the girl Curtis then asked her if her parents were how, she said they were not, and he attacked her and attempted to rape her. Unbeknownst to Curtis, however, her brother had called the police who arrived on the scene.