Corruption in order is killer (9)

I believe the answer is:

garrotter

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

'is killer' is the definition.
(I've seen this before)

'corruption in order' is the wordplay.
'corruption' becomes 'rot' (I've seen this before).
'in' indicates putting letters inside.
'order' becomes 'garter' (I am not sure about this - if you are sure you should believe this answer much more).
'rot' inserted within 'garter' is 'GARROTTER'.

Can you help me to learn more?

(Other definitions for garrotter that I've seen before include "Killer" , "Executioner" .)

I've seen this clue in The Independent.

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.