ATC Watcher...
I'm not sure why you conclude the collision occurred in Mali's airspace, and therefore there is "no need to mention Senegal ATC".
The information we have so far (which is admittedly very little indeed) includes a Lat and Long position given by the Senegalese which puts the B737 in Senegal's airspace when the two aircraft "crossed".
The Senegalese statement also says the CEIBA B737 was "about to be handed off" to Bamako.
So, it is more likely the collision ocurred in Senegal's airspace, though that is not certain of course at this point.