ὡς δὲ γνῶναι αὐτὸν ἐν οἵῳ κακῷ ἦν, ἰθέως καλέειν τὸν ἀδελφεὸν καὶ δηλοῦν αὐτῷ τὰ παρεόντα, καὶ κελεύειν τὴν ταχίστην ἐσδύντα ἀποταμεῖν αὐτοῦ τὴν κεφαλήν, ὅκως μὴ αὐτὸς ὀφθεὶς καὶ γνωρισθεὶς ὃς εἴη προσαπολέσῃ κἀκεῖνον.
The infinitive γνῶναι doesn't look like any use of the infinitive that I have so far encountered. Given the context I would expect a genitive aorist participle rather than an aorist infinitive. What am I missing?