One imprisoned as murderer (4)

I believe the answer is:

cain

I'm a little stuck... Click here to teach me more about this clue!

'murderer' is the definition.
(Biblical figure)

'one imprisoned as' is the wordplay.
'one' becomes 'i' (Roman numeral).
'imprisoned' is an insertion indicator.
'as' becomes 'can' (I can't justify this - if you can you should give a lot more credence to this answer).
'i' inserted inside 'can' is 'CAIN'.

Can you help me to learn more?

(Other definitions for cain that I've seen before include "The first known murderer" , "Eldest son of Adam, Eve" , "Abel's brother" , "First murderer reported in the Bible" , "Brother of Abel" .)

I've seen this clue in The Globe and Mail and The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.