I think this is what makes the book so relevant and exciting. As readers, we each take a different stance. Is he guilty? Is he innocent? The important thing is to keep up with why you think he's innocent. You could be absolutely correct, but remember that you have to be able to articulate why you think this way. Keep in mind who your narrator is, whose thoughts your reading. Do we connect with our narrator? Does that make it harder to see him as guilty?
An excellent debate topic for your class. Look back at those instances where you think he shows his innocence.
I am sure that you would find many people would agree with you, and many other people would not agree with you. If you are looking for support to your stand, I agree. I do not think that Steve Harmon is guilty. The flashbacks provided, his journal (movie script), and the point of view he offers leads me to believe in his innocence.
As for Steve's possible guilt, there are a few times in the novel where Steve seems to float a little too much during his narrative.
Overall, it simply depends if you (as a reader) can relate to him and feel sympathy. If you do, you will most likely feel as if he is innocent. If you fail to relate and sympathize , you will most likely find him guilty.