ἔγωγε δὲ φοβοῦμαι, ὦ ἄνδρες, μὴ ἂν εἴη καὶ Δημοσθένης τις ἀδύνατος εἰπεῖν τὴν τῶν ἀδικημάτων δεινότην τῶν τρίακοντα· οὐ γὰρ μόνον ἀπέκτειναν τοὺς ἀναιτίους ὧντινων αἱρήσονται τὰ χρήματα, ἀλλὰ καὶ εἰς τοσοῦτον ἧκον αἰτίας ὥστε προὔδωκαν τοὺς τε φίλους καὶ τοὺς προσήκοντας θᾶττον ἢ τοὺς ἔχθρους. τοσαύτη γὰρ οὖν ἡ μοχθηρία τούτων ὥστε διήρπασάν ποτε οἱ τριάκοντα καὶ τοὺς σφετέρους.
I am afraid that even a Demosthenes would be unable to express the heinousness of the crimes of the Thirty. Not only did they kill the innocent in order to take their money, but they reached such a level of criminal behavior that they betrayed their own friends and relations even more quickly than their enemies. In fact, their corruption was so extensive that the Thirty began to prey upon their own members.
(To be clear, I composed the Greek from the English. Not the other way around.)