Religion endlessly engrossing murder victim's girl (8)
I believe the answer is:
isabella
'girl' is the definition.
(I've seen this before)
'religion endlessly engrossing murder victim's' is the wordplay.
'religion' becomes 'shiah' (Shiah is an example).
'endlessly' indicates the central letters (the ends of the words are removed).
'engrossing murder victim's' becomes 'sabella' (I can't explain this - if you can you should give a lot more credence to this answer).
The centre of 'shiah' is 'i'.
'i'+'sabella'='ISABELLA'
Can you help me to learn more?
(Other definitions for isabella that I've seen before include "A queen of Spain" , "Henry VIII's first mother-in-law" , "Wife of Edward II" , "Spanish queen who financed Columbus" , "Mother of Edward III" .)