Unit is related to Society. 
Saving is related to Rescue. Rescue is the opposite of Arrest. Killing can cause/lead to Arrest. one thing you do when you Killing is Scream. 
Unit <--RelatedTo--> Society 
Saving <--RelatedTo--> Rescue <--Antonym--> Arrest <--Causes-- Killing --HasSubevent--> Scream 