In order to get this achievement you have to set up the correct conclusions:
- Two people
- Imitated robbery
- Randalls blamed
- Poker blow
- Sailor background
- Domestic violence
- Acquainted with a sailor
- Croker's involvement
You then have to choose the "Justice"-option to get to the right ending.
There will be a critical moment where you have to grab the hand of the Captain (aim on his hand with the left stick and then press "A" when the circle turns blue). This will be followed by a QTE - i had to quickly tap "A" and then press "Y".
(please message me if the QTE is different for you)
The achievement should pop after successfully disarming the Captain.
Edit: User "VeiRon" said the following: You can either choose arrest or absolve,the ending does not change,he will still pull out a gun and try to kill himself.