The ending was explained......
We know from the step-mom talking on the phone that the black kid was ok and that crazy guy only hallucinated killing him.
We also know that they probably ended up hiding the murder and Gere likely said nothing.
The first clue is that when gere found out his Bill passed, they were so elated that they had temporarily forgotten about black kid - revealing the truth of his priorities.
The second clue is that earlier in the film, crazy guy narrated and said something like “ you are going to want to like my brother, but don’t be fooled- he will end up disappointing you”. This means that gere will likely loose his nerve and go from confessor to fellow conspirator, and he will likely try to contain the guilt of black kid by talking him down - thus dissapointing the audience by placing his career and recent success over the moral imperative of black kid.
At first I felt cheated by the ending, but after giving it a moment, it’s kind of clever how they gave you all the information you need.