Well if they can't find hundreds of tonnes of CBW weapons, nuclear research programmes, Saddam or Bin Laden why would you expect them to find a single 727 in the African Bush.
Perhaps the African equivalent of the Gippos took it for scrap one night. On the other hand if you are going to nick several thousand gallons of aviation fuel it has to be easier to take it already loaded than to syphon it out amd take it away in jerry cans strapped to the handlebars of your bike.
It wasn't the local equivalent of Rag week when it got pinched was it?