Why the Longbottoms were tortured

[MrNipha]

No: HPFGUIDX 72215

I was thinking about Bellatrix's speech that Harry views in the
pensieve, about her and her cohorts trying to find out what happened
to  the Dark Lord by torturing the Longbottoms.  Yes, the Longbottoms
were Aurors, but my thought (pre-OoTP) was why would they know what
happened to Voldemort?

The thought just came to me -- the prophesy.  The DE's probably knew
about the prophesy and that they (including Voldemort) only had
information on the first part of the prophesy.  Since Voldemort's
attempt to kill Harry had gone wrong, they might have figured that the
rest of the prophesy might give them a clue of what happened to, and
perhaps where to find Lord Voldemort.  Who to ask?  Dumbledore knew
the full contents of the prophesy, but he wasn't someone they could
mess with. However, if Dumbledore told the parents of the possible
"One", the DE's could get the information from them.  The parents of
the boy who had vanquished Voldemort were dead, but the parents of the
other possible boy referred to in the prophesy were not -- Frank and
Alice Longbottom.

Either 
1. Dumbledore did not tell the Longbottoms the whole prophesy, 
2. the Longbottoms' resisted telling the DE's, or 
3. the DE's were not satisfied with the answer the Longbottoms gave
them because it didn't tell them what they wanted to know -- what was
to happen to the Dark Lord after he was vanquished.

I think it was 3.  Lucius Malfoy says in the Prophesy Room to Harry
that the Dark Lord wondered why Harry didn't go to retrieve the
prophesy when he (V) first showed him (H) its location to hear it for
himself.  Voldemort and the DE's assumed that Dumbledore had told
Harry, like he had told Harry's parents and Neville's parents. 
Voldemort ascribed his own motivation (to hear the prophesy for
himself, not second-hand as second-hand knowledge had already cost him
once) to Harry, and only resorted to using the fake image of Sirius in
danger after Harry didn't act.

Any thoughts?

MrNipha