What is the basis for the doctrine of the Trinity in the Book of Mormon?

The Community of Christ – formerly the "Reorganized Church of Jesus Christ of Latter Day Saints" – is a rather unique branch of Christianity in that it stems from the LDS Church, recognizing the Book of Mormon, but is also Trinitarian in its beliefs. It seems to follow from this that they must conclude that the Book of Mormon affirms the doctrine of the Trinity and does not teach eternal progression like the LDS church teaches. My question, then, is what is the Book of Mormon basis in support of the doctrine of the Trinity?