If you go to Flightaware you can see the plane accelerated from 598 to 613 MPH in last few minutes. Its last reported speed is the fasted recorded of the entire flight. I thought that was strange when I first saw this.
But no change in altitude, just speed?
Pure speculation:
Maybe a bomb went off, depressurized the plane and caused damage to the controls. Then maybe the pilots struggled with the controls, forgetting to put on oxygen masks and lost consciousness. The plane may have been on autopilot and continued to fly until it broke up. The speed gain may have been due to control damage from the bomb.