The distance between the departure point and the destination appears to be on the very edge of, if not outside of the flight envelope and that does not include any fuel for an alternate or reserve. It appears to me they pushed this flight to the absolute extremes of range, with no plan B. Why didn't they report the critical fuel state? Simple, IFR with no alternate and no reserve fuel will get the authorities attention. Nobody wants to deal with that.
I don't know what really happened and I don't want to be critical without cause but this doesn't look good. The same aircraft apparently made the same trip (in the opposite direction) earlier in the month. Recorded flt time was 4:33 hrs/min. This flight appears to have ended at 4:40 hrs/min. Looks like a fuel stop at Bogota would have been more than prudent [There goes the profit margin]. Pressure from the company? Who knows, but pilots just don't do that sort of thing without a reason.
So much for my .02 cents worth of speculation, for which I am sorry. We'll have to wait and see but it should not take too long to determine if those engines were running at impact or not. I grieve for everyone, especially the pilots. Fate is the Hunter.