Answer: Reciprocity
Explanation: Reciprocity is an act of kindness towards someone that is done with a belief that if I do good to you , you are likely to return the favour and do good to me.
If someone has been good to you it is likely that you will want to be good to them too, such as this inmate who has been well behaved and who has not caused problems for the officer.
Since he has been good the officer wants to be good to him . That is reciprocity.