interrogative pronouns introducing indirect speech

In Socrates’ reply[1] to the question  “What sort of indictment has been brought against you?”  we see indirect discourse[2] (oratio obliqua) introduced by a verb of speaking φησιν followed by a verb of knowing οἶδε. The two interrogatives τίνα τρόπον and τίνες introduce the content, what is claimed to be known by the young man bringing an indictment against Socrates. Interrogative pronouns introduce both direct and  indirect speech[3] (questions).

ἐκεῖνος γάρ, ὥς φησιν, οἶδε τίνα τρόπον οἱ νέοι διαφθείρονται καὶ τίνες οἱ διαφθείροντες αὐτούς. 

“For he says he knows how the youth are corrupted and who those are who corrupt them.”

[1]Plato  Euthyphro
Stephanus page 2, section c, line 4
English Tanslation: Harold North Fowler

Σωκράτης
ἥντινα; οὐκ ἀγεννῆ, ἔμοιγε δοκεῖ: τὸ γὰρ νέον ὄντα τοσοῦτον πρᾶγμα ἐγνωκέναι οὐ φαῦλόν ἐστιν. ἐκεῖνος γάρ, ὥς φησιν, οἶδε τίνα τρόπον οἱ νέοι διαφθείρονται καὶ τίνες οἱ διαφθείροντες αὐτούς. καὶ κινδυνεύει σοφός τις εἶναι, καὶ τὴν ἐμὴν ἀμαθίαν κατιδὼν ὡς διαφθείροντος τοὺς ἡλικιώτας αὐτοῦ, ἔρχεται κατηγορήσων μου ὥσπερ πρὸς μητέρα πρὸς τὴν πόλιν. καὶ φαίνεταί μοι τῶν πολιτικῶν
Socrates

What sort? No mean one, it seems to me; for the fact that, young as he is, he has apprehended so important a matter reflects no small credit upon him. For he says he knows how the youth are corrupted and who those are who corrupt them. He must be a wise man; who, seeing my lack of wisdom and that I am corrupting his fellows, comes to the State, as a boy runs to his mother, to accuse me. And he seems to me to be the only one of the public men who begins in the right way; for the right way

[2] Most grammars would call this an indirect question, but it functions like indirect discourse. See G. L. Cooper, Attic Greek Prose Syntax, v.1 p553, 1:51.17.0

[3] See G. L. Cooper, Attic Greek Prose Syntax, v.1 p554, 1:51.17.2.