They told him that it is dangerous to live in Hashem's Holy Land and not obey the Torah.
The king of Assyria therefore decided to send some Kohanim of Israel to teach the Cuthites how to keep the Torah.
When he took the Ten Tribes of Israel away from Samaria, he brought the people called the Cuthites to replace them. Since the Cuthites settled in the area known as Samaria (Shomron), they later became known as the Samaritans (Shomronim).
When the Cuthites were first relocated into Samaria, they were being killed by plagues of lions, and they did not know what to do about it.
They rejected the Books of Samuel and Kings because those Books supported King David, and because they were written by the Prophets Samuel, Nathan, and Gad, who strongly supported King David.
They rejected the Book of Ruth because it told of the ancestry of King David.
So they created their own book, which they call Joshua. The Persians eventually gave the Jews permission to rebuild the Holy Temple.