Complex sentence: Agnew had promised to cause the family harm and afterwards strange phenomena was alleged to have occurred at the house for over two years such as the mysterious cutting of thread, strange whistling noises and stones being thrown.
Split into simpler sentences: Agnew had promised to cause the family harm and over the next two years strange phenomena was alleged to have occurred at the house. This included the mysterious cutting of thread, strange whistling noises and stones being thrown.