> Ground observers reported the aircraft had been delayed for about two hours for work on the left hand engine (engine #1), the engine #1 separated during the takeoff run, the center engine emitted streaks of flames, the aircraft impacted a UPS warehouse and ploughed through other facilities before coming to rest in a large plume of fire and smoke.
So the tl'dr is: the leading very preliminary theory is that the MD-11's left engine fell off the wing just like https://en.wikipedia.org/wiki/American_Airlines_Flight_191 (a DC-10, the immediate predecessor of the MD-11) which was caused by maintenance errors weakening the pylon structure holding the engine.
What strikes me as odd is that this looks like the "naked" engine, without the cowling/nacelle that usually surrounds it? Anyway, if an engine departs the aircraft shortly after (last-minute) maintenance was performed on it, that's indeed suspicious...