Complex sentence: According to Atkins and Kasabian, Manson disappeared up the driveway and returned to say he had tied up the house's occupants; then he sent Watson up with Krenwinkel and Van Houten.
Split into simpler sentences: According to Atkins and Kasabian, Manson disappeared up the driveway and returned to say he had tied up the house's occupants. He then sent Watson up with Krenwinkel and Van Houten.