I haven't seen this mentioned yet, but accordng to this article in the NY Times, "the Russian authorities have, unusually, asked the F.B.I. for assistance in the investigation, according to senior American officials."
"Russia has asked the F.B.I. to help analyze forensic evidence from the crash to pinpoint its cause, American officials said. The F.B.I. and its Russian counterpart, the Federal Security Service, often collaborate against common enemies like Al Qaeda and the Islamic State, but the request for help on the plane crash was seen as unusual."
http://www.nytimes.com/2015/11/08/wo...ref=world&_r=0
OK, here's the full article:
http://www.nytimes.com/2015/11/08/wo...html?ref=world