What gave Edwin and Garvey a deep understanding of Cole's problems?

In Chapter 15, the Circle of Justice meets to decide whether or not Cole will be returned to the island after he heals. When everyone else wants to end Cole's time on the island, Edwin challenges them by declaring that although Cole hasn't had a complete change oh heart, he has had a change in direction. 

The crux of the decision lies on whether there was actually a Spirit Bear on the island, or if Cole is just lying again. Edwin declares that a group of fishermen claimed to see a Spirit Bear off of the island where Cole was stationed a day after Cole left the island.

A central theme explored most fully in this section, thus, is that of truth. Up to this point, Cole has been consistently lying. He lied to the Circle about his intention to reform himself, and he lied to Edwin and Garvey that he would remain quietly on the island. Now, however, Cole is placed in the curious position of telling the truth having established a reputation for deceit. The impact of truth telling goes beyond Cole to the very striking transformation of his mother into a truth-telling and caring woman for the first time in Cole’s life. She finally stands up to Cole’s father and tells the truth about his abuses of Cole to the police, and she finally opens up to Cole so that they can have a true relationship—or at least begin one.

Ultimately, however, the most important effect of Cole’s truth telling is the trust built between Cole, Edwin, and Garvey. It is only through the advocacy of the latter two that Cole is able to gain his ultimate verdict to return to the island and complete his sentence. The author uses intense bursts of dialogue to convey the tenuous trust that is building between them, particularly in their dialogue towards the end of Chapter 15 where Edwin reveals that he has convinced the circle to release Cole to the island again.