Who killed Lily and James Potter?

[addictedtobass2003]

No: HPFGUIDX 55427

Events that occurred on 31st October 1981, and their order are still 
unclear to the reader (in my opinion).
Priori Incantatem reveals the spells discharged from a wand in 
reverse order, but not who cast them.
In GoF chapter 34, it reads as if Harry was attacked first (because 
he never came out of the wand, and we presume that if Harry would 
have endured, he would have appeared.  The next event that happens 
is the death of James, and then of Lily.  If Voldemort was left 
almost powerless by Harry, how could he have killed Lily and James?  
Was there someone else present at the time to cast the spells with 
Voldemort's wand when Voldemort had been defeated?

"Voldemort killed James and Lily, then tried to kill Harry." 
     -- JKR on the Diane Rehm Show, October 20, 1999.  

Why in PS/SS does it also lead you to believe James was killed, then 
Lily (whilst trying to protect Harry), and then Harry was attacked?

I'm not entirely sure if I am interpreting the whole thing wrong, or 
if it is a misprint.  I'm new to the board so I'm still catching up 
on past messages, so if this query has already been answered, I 
apologise, but would appreciate a reply nevertheless.

Also does anyone have any theories on why Voldemort was so 
determined to kill Harry in the first place, I would be interested 
to read them.

Thanks

addictedtobass2003

"We are only strong as we are united, as weak as we are divided."