From a Moscow Times article today:
"So far there are no signs of terrorist acts taking place on board either plane," FSB spokesman Nikolai Zakharov said.
Investigators rolled out evidence disproving a terrorist attack. They said none of the recovered bodies had burns -- which would have been an indication of an on-board explosion. The hijack alert from the Sibir Tu-154, confirmed by air traffic controllers and Sibir, was in fact an SOS call. And they said their investigation will not focus on terrorism but violations of civilian aircraft rules.
http://www.moscowtimes.ru/stories/2004/08/26/002.html
Seems all a bit fishy.