Was Eve stealing an apple an unprecedented crime? (5,7)

I believe the answer is:

first offence

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

'was eve stealing an apple an' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'unprecedented crime?' is the wordplay.
'unprecedented' becomes 'first' (I've seen this in another clue).
'crime?' becomes 'offence' (offence is a kind of crime).
'first'+'offence'='FIRST OFFENCE'

Can you help me to learn more?

I've seen this clue in The Guardian.

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