Having a long-term interest in these craft I tried to find out a little more from the Colombian authority (Aerocivil).
Not being a Spanish speaker has made that difficult but I did see several references to this being a training flight on other sites. It could be that 'training flight' has become 'test flight' during the course of translation to English(?).
If so that may add a further possible factor in the mix of potential issues that caused this crash. In any event if someone who reads English + Spanish is able to navigate Aerocivil's site
here it would be useful to know if they have a reasonable accident investigation branch and, if so, whether there is any further information (and/or when such information might be likely to be published).
One thing that did seem to survive translation across several reports is that the crash appeared to occur early (approx 5 mins) into the flight.
As a result and in thinking about the possible causes I did wonder if some of the control locks could still have been in place. Although comment has been made about maintenance quality these are tough birds and to have something fail so catastrophically that the machine would crash is probably not quite at the top of my 'likely' list (although I quite accept it as a possibility).