Snape's Hiring

[Julie]

No: HPFGUIDX 86291

Hello, everyone.
I've been lurking for months enjoying the really insightful and 
informative discussions on different aspects of the Harry Potter 
books.  Many of you know the characters and books backwards and 
forwards, its amazing and a lot of fun to follow (and very humbling)!

I've a question that I hope someone can help me with, regarding the 
end of Goblet of Fire and Order of the Phoenix.

I've read each book several times (US edition), but can't seem to 
find the information.  I've been told through another list that JKR 
clearly stated in O of P that Severus Snape's presence teaching at 
Hogwarts was ordered and approved of by Lord Voldemort in order to 
spy on Dumbledore.  (She/he is emphatic that this is one more piece 
of evidence that Snape was at the rebirth in the graveyard and is 
really ultimately loyal to Voldemort and not Dumbledore.) 

I've looked and looked but I just can't find this information 
anywhere (nor conclusive proof that SS was at the cemetery).  I would 
hate to think that I've misread such important points.  Since many of 
you really know the books inside and out, would someone be willing to 
point me in the right direction to that passage in the book?

Thanks,
Julie