LXX Num 35:28

ἐν γὰρ τῇ πόλει τῆς καταφυγῆς κατοικείτω ἕως ἄν ἀποθάνῃ ὁ ἱερεὺς ὁ μέγας· μετὰ τὸ ἀποθανεῖν τὸν ἱερέα τὸν μέγαν ἐπαναστραφήσεται ὁ φονεύσας εἰς τὴν γῆν τῆς κατασχέσεως αὐτοῦ.

because the manslayer must remain in his city of refuge until the death of the high priest. Only after the death of the high priest may he return to the land he owns.