Not everyone finds Arnold's statements convincing
Agreed, and I think one of the main reasons why he's taken so seriously is because of what we can see in the Moorman photo - Arnold being in and around this area.
Anyway, here's an interesting interview with Arnold. He discusses what he did, what he saw etc. You might find it interesting.
I've always found this website particularly in-depth also.
EDIT: In regards to Arnold's credibility, here's a snippet from the above source:
Some researchers have doubted Arnold's testimony but it has been supported by the testimony of Ralph Yarborough who told a newspaper reporter from the Dallas Morning News: "Immediately on the firing of the first shot I saw the man you interviewed throw himself onto the ground. He was down within a second of the time the shot was fired, and I thought to myself, 'There's a combat veteran who knows how to act when weapons start firing.' "
This is all discussed, and more, in the above interview.
edit on 14-6-2011 by Rising Against because: (no reason given)