ἐκεῖνος may refer to any person other than the speaker and the person addressed; and may be employed of a person not definitely described, but referred to in a supposed case. It is even used of the person already referred to by αὐτός in an oblique case:
ἂ_ν αὐτῷ διδῷς ἀργύριον καὶ πείθῃς ἐκεῖνον
πρὸς μὲν ἐκείνους οὐκ εῖπεν ἣν ἔχοι γνώμην, ἀλλ' ἀπέπεμψεν αὐτούς
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].