The correct option is C Have been identified
Here, 'have been identified' in present perfect continuous is correct because it is used to indicate an action that started at some point in the past
and may or may not be complete.
'Has been identified' is incorrect because those killed are two in number (plural), not one (singular).
'Was identified' in past continuous is incorrect because it is used to indicate uncompleted action in the past (with or without time reference).