AFAIK there has been no clear cause published and I would not expect a proper investigation report to be published in less than a year.
If we assume that there was an engine failure after takeoff this should not have caused a crash in a twin engined aircraft.
This leads to two possibilities ( there are other less likely causes ) :-
1) The pilots failed to take the correct engine failure actions.
or 2) The aircraft took off below Vmc (minimum single engine control speed).
There are several reasons why Vmc might not have been achieved.
a) Airstrip too short for safe operation of the aircraft type.
b) Overweight.
c) Engines not delivering full power.d) Wet or muddy grass or dirt airstrip.
e) Brakes not properly released.
f) Failure to select full power.
g) (other less likely.....)
I would normally expect the cause of failure to acheive Vmc to be a combination of several of the above. For example the strip length being marginal for the aircraft type and the aircraft being overloaded.
I suggest that you ask your pilot to explain his thoughts and that you learn more about safe operating best practice and the ways that many african operators push their luck until the inevitable eventually bites.