So, it is now being reported that the captain turned off the fuel to both engines. It is hard to imagine this was a mistake, given a) the experience and b) how hard it is to do this by mistake. Apparently, you have to fiddle with the switches (push them in, then flip them down). This leads one to believe it was a suicide. The voice recording has the pilot speaking plainly while the copilot freaks out, asking him why he shut down the fuel to both engines.