STEPHANOPOULOS: You say you can't talk too much about the investigation, but we are learning a fair amount about Major Hasan in the last couple of days. And it appears that there were several warning signs they either could have or should have been caught.
His fellow students and here in Bethesda, Maryland, say that he had anti-American rants at various presentations. The FBI has found some Internet postings by a man with Mr. Hasan's name, very inflammatory, praising suicide bombers.
And one of the major's fellow students has been especially concerned by what he said. He said that it was very clear to him, and his name is Val Finnell, that -- and that he had complained to administrators at a military university about these anti-American rants. And the AP story that quotes him goes on to say that Hasan's fellow students complained to the faculty about Hasan's anti-American propaganda, but said a fear of appearing discriminatory against a Muslim student kept off the students from filing a formal complaint. Is that true?
CASEY: I think we need to be very careful here about speculating based on anecdotes like that. We are encouraging all of our soldiers and leaders that may have information pertaining to the suspect to come forward with that information to the criminal investigation division and to the FBI. So, I realize there is a lot out there. We all want to know what happened and what motivated the suspect, but I think we need to be very, very careful here in these early days to let the investigation take its course. These are professionals and they will sort through this.
STEPHANOPOULOS: So it's fair to say that right now, you can't rule out anything. We don't know if this was an act of premeditated political terror, or if this was a case of someone who just snapped.
CASEY: I think you are exactly right, and I don't think we should speculate on one or the other or any other possibilities.
STEPHANOPOULOS: One of the things this does raise, though, is the special challenge paused to all of you by Muslims in the military. There are only about 3,000 Muslims in the military right now, and on the one hand, you want to recruit Muslims. There is a great need for Muslims in the military right now. On the other hand, this is not the first case we've seen of fratricide by someone with a Muslim background in the military. How do you deal with this challenge?
CASEY: Again, I think that's something else we need to be very careful about, and I think the speculation could potentially heighten backlash against some of our Muslim soldiers. And what happened at Fort Hood was a tragedy, but I believe it would be an even greater tragedy if our diversity becomes a casualty here. And it's not just about Muslims. We have a very diverse army. We have a very diverse society. And that gives us all strength. So again, we need to be very careful with that.