τοῦ αὐτοῦ γε ρήτορος ἐϰ τῆς νήσου ἥϰοντος: "from the very same orator who arrived from the island."
Ἀϰούετε: present active imperative. When you begin a direct quotation, you capitalize the first word, in Greek as in English.
πολῖται: We have to ask you to pay extra special attention from now on, JM, to the difference between singular and plural! And notice the English spelling of "citizen."
ἐπειδὰν ἥϰωσι = "whenever (as soon as) they should arrive." The subject of ἥϰωσι is οἱ φονεῖς.
λαβόντες: aorist active participle of λαμβάνω. "having taken," "after taking."
δίκην γράψομαι αὐτοὺς πάντας = "I will bring an indictment against them all."
πως = "somehow or other."