Estar+Ser+gerund

Question

I find this concept a bit confusing and awkward.  "Las joyas estaban siendo robadas por el ladron."  I feel it should be simpler, "las joyas fueron robadas por el ladron."

Accepted Answer

Hola Donald
The passive voice using compound tenses and progressive tenses in English may not be that common and may tend to be simplified to simpler structures, but in Spanish we use this type of long structure to convey the "continuity". By saying "were being stolen..." (estaban siendo robadas) we place ourselves at that moment in the past and see the action as something "happening" then. If we simplified it with "were stolen" (fueron robadas) then we don't see the continuity of that action. 
Saludos
Inma