As for the actual content in question - here's an archive of a tweet of them boasting about having Buk missile launcher, the tweet was later deleted:
http://web.archive.org/web/20140707150151/https://twitter.co...
Here's a screenshot of the VK account where their (now former) commander and defense minister (and allegedly "ex" FSB member) claimed the downing of a Ukrainian plane, later the content was deleted:
http://i.imgur.com/fi4Zkx6.png
The Wikipedia article covers all that in depth:
https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_17
