Complex sentence: When he found the group was carrying an Elf-made blade which had killed many Goblins he gave orders for them to be imprisoned and tortured and tried to attack Thorin, but was slain by Gandalf.
Split into simpler sentences: When he found the group was carrying an Elf-made blade which had killed many Goblins he gave orders for them to be imprisoned and tortured. He tried to attack Thorin, but was slain by Gandalf.