DotCommunist
So many particulars. So many questions.
Just a hypothesis: attempted hijack, someone started shooting (either security or hijacker) and the fuselage was perforated by bullets. Depressurisation would almost certainly occur and perhaps fast if there was a widow hit?
The US and Israel certainly use armed security although how that works bullet wise who knows.
air marshalls. iirc they carry non lethal deterrents because nobody wants a sawn off being discharged in a pressured aircraft