כִּ֣י בְעִ֤יר מִקְלָטוֹ֙ יֵשֵׁ֔ב עַד־מ֖וֹת הַכֹּהֵ֣ן הַגָּדֹ֑ל וְאַחֲרֵ֥י מוֹת֙ הַכֹּהֵ֣ן הַגָּדֹ֔ל יָשׁוּב֙ הָרֹצֵ֔חַ אֶל־אֶ֖רֶץ אֲחֻזָּתֽוֹ׃
because he must remain in his city of refuge until the death of the high priest; but after the death of the high priest the manslayer may return into the land of his possession.
Read kabbalistic (mystical) interpretation of Numbers 35:28: and classical mystical sources.