With all due respect, I tend to disagree with my fellow armchair detective, if I may.
1) Plane was in relatively good condition and maintained adequately at least.
I'd rather state it as "aircraft-related paperwork was in good condition and maintained adequately". For a company that already had a hull loss due to inadequate maintenance (RA-85588, fire started by a short circuit), I wouldn't discount the possibility of taking some fatal shortcuts in maintaining their aircraft, as it did happen before.
2) Crew is experienced and rested
Experienced - yes, rested - how would you know for sure? I tend to agree though that crew action or inaction was, most likely, irrelevant to this particular accident.
3) No suspicious passengers onboard, no major delay or any other inconvenience through ground ops reported
4) T/O without issues and begin climbing OK
That's what we've been told so far, correct.
5) When reached about intended FL but before leveling something very brief (fraction of seconds) and violent happened INSIDE, plane was broken in parts and falls down.
Fair enough, although I wouldn't be so certain about the event taking "fraction of a second". It could just as well take, say, five or ten seconds, and again, one cannot really discount the possibility of a slowly developing, undetected malfunction that finally manifested itself as an in-flight breakup. (For once, imagine cargo hold smoke detectors inoperative.. not exactly an impossible scenario)
5.1) This event was so short that crew have no time to complete any action, so it's not stall or similar.
Or, alternatively, any actions of the crew were not enough to prevent the tragic outcome. Or, again, the crew could be unaware of a developing problem until it became too late. In any case, I agree that it's reasonable to discount the crew action as a direct cause of this event.
5.2) This even was followed (and possible is cause) of tail section detachment
Tail sections don't usually get detached by themselves, so this can't be attributed as a direct cause. An airplane that may, all of a sudden, shed its tail section by itself, is not exactly airworthy.
With all due respect, and no unconstructive criticism intended.