However horrific the civilian plane's shooting down is, i don't think accidental shoot down would qualify as a war crime. If anything, the celebratory message about supposed successful shooting down of one more military cargo plane confirms that the rebels, it it were rebels' missile, were intending to shoot at an enemy military target .
"Murder, extermination, enslavement, deportation, and other inhumane acts committed against any civilian population, before or during the war..." is a crime against humanity.
Wrt. the right [more precisely lack of it] to be forgotten and war crimes : http://en.wikipedia.org/wiki/Convention_on_the_Non-Applicabi...