Of course it's really early so you have to be very careful as to making judgements at this point, but if it really is pilot murder/suicide there is some (limited) precedence:-
There is debate in both flights as to whether it was murder/suicide, but the evidence is totally overwhelming that it was. Horrific but thankfully massively rare (as you might expect.) I do hope this isn't the cause here :(
* An EgyptAir flight in 1999 - http://en.wikipedia.org/wiki/EgyptAir_Flight_990
* A Silkair (Singapore airline) flight in 1997 - http://en.wikipedia.org/wiki/SilkAir_Flight_185
There is debate in both flights as to whether it was murder/suicide, but the evidence is totally overwhelming that it was. Horrific but thankfully massively rare (as you might expect.) I do hope this isn't the cause here :(