You are refering to a crash of an Itavia DC-9 of the coast of Italy. You can get some details and a load of links on this site. There still is no answer what happened other than that the plane broke up mid-air.

NATO has a radar station nearby, but has been unwilling to hand over the information. In fact, NATO has been death silent about the whole of the matter other than the usual ambiguous bull we have grown to love from militaries worldwide.

The most likely cause is that NATO planes shot it down by accident. Two Libyan fighters where at the time intercepted by 3 Italian, 1 French and 1 US fighters. Warships where in the area as well. The Libyans where flying close to the Itavia jet to mask their radar signature and make them harder to hit without damaging the Itavia.

It would appear that the Libyan planes got fired upon. Another option could perhaps be a mid-air collision with the Itavia and one or both of the Libyans. However, I seem to recall that this theory was discredited.

http://aviation-safety.net/specials/ustica/

The only reason to be silent and refuse to release information is because you have something to hide.

By simply refusing to relase info, NATO have as good as confessed to shooting it down.