Can the debris pattern from a crash site confirm explosion as the cause of a crash?
No, not an explosion, just break-up.

The debris field can prove if some parts of the aircraft broke off in the air, before the main impact. However the aircraft can break up also if the pressure vessel fails, if intense fire compromises the structural integrity, or due to mid-air collision.

And on the other hand, an explosion can make the plane uncontrollable without breaking off any large parts e.g. if it severes the hydraulic lines (which can also start fire as the hydraulic fluid is flammable).

An explosion can only be proven by collecting pieces of the wreckage and looking for traces of spalling, shrapnel damage and traces of an explosive.