Since this is an all-electric train (and all electronic speed/motor control unlike older electrics with relay stepped transformers) it would seem to boil down to two possibilities.. 1)the electronics was told to accelerate by physical command or 2)the electronics accelerated on its own without a physical command.
For the first instance, the throttle must be advanced. I've never been in the cab of an operating toaster, er, electric locomotive, but in a diesel it's referred to as 'notching up' (from idle up to 'run 8' - unless they've changed terminology on me) which (again on a diesel) increases the rpm's of the diesel which in turn increases the electrical output to the motors on the trucks. I would assume that a similar action is required on an electric which in this instance would generate an input to the electronics to cause acceleration.
If the investigation reveals that the electronics in fact received such an 'accelerate' signal from the throttle it can safely be assumed that the engineer for whatever reason physically advanced the throttle. Which will of course then require finding out why. And we will probably need tinfoil hats...
For the second instance, electronic drives (actually ANYTHING man-made) are not 100% fail safe and strange and non-salubrious manifestations do occur which of course could/would be the result of a massive fault of some sort that managed to bypass all sorts of fault-protection devices. In a normal fault situation most electronic drives shut themselves off but a long time ago I quit saying 'it can't do that' as I witness the piece of electronica I was troubleshooting do something that it absolutely was not supposed to be capable of doing and remain online. (Wearing the Field Engineer's hat means that when that happens you are supposed to figure out why so you can call up the 'desk engineer' and say 'Boy, did you blow it', or words to that effect - and then explain why so that it gets fixed before some lawyer gets involved...)
In most applications the indications of such a cataclysm in the electronica will be buried in a fault log somewhere in the bowels of the beast and may take a bit of time to decypher the info - and by then the ozone and smoke will be long gone.
In reading up on the ACS-64 and the Siemens blurbs, this piece of technology has a rather extensive diagnostics built into the software. Again, nothing is cast in stone here, but it can be a really safe assumption that if there was a fault of some sort that caused such an event in the Siemens package it would show up on the diagnostics log somewhere, although maybe not so clearly defined.
IF there is such an instance either we will hear of it as a result of the portion of the investigation that is made public, or there will be some sudden and very quiet revision notices issued to affect modifications to the design that will not be publicized but will leak out in the future.
If there is a third possibility, I'm not seeing it...
The speed is the answer I think he tried to suicide but changed his mind.He is a very strange person.JMO