I agree that it was probably Deepak. Here's a question:
Did Deepak get upset because he believed he might be caught, or did Deepak get upset because he knew he was about to be set up? With so few sustantiated facts we can only guess as to what that reaction means. If they could only find something else in that same area that points to the 3 boys committing a crime, I think we will all agree he was mad because he was about to get caught. As it is, we really don't know for sure. We all have our opinions, but we don't know. It's very frustrating.
I think what might have happened is that Joran and Natalee developed a romance over the course of a few days and Deepak was jealous. I remember seeing Joran's website before it was taken down and he seems to have been very popular with the young tourist ladies. Deepak may have been smoldering in jealousy for some time. Maybe if and when Natalee rebuffed him he thought it was because he wasn't white and it enraged him even more, as we often see race issues enrage people in the US. He proceeded to manhandle her and she died, probably by accident, and all three boys were bound in a conspiracy of silence.
Whatever happened I just don't see a death happening by anything other than accident. I know people here have pieced together rumors and innuendos and have come up with them being worse than Saddam Hussein, but I haven't seen any realistically believable evidence that these boys are murderous tyrants.