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.
KJV
Because he should have remained in the city of his refuge until the death of the high priest: but after the death of the high priest the slayer shall return into the land of his possession.
ASV
because he should have remained in his city of refuge until the death of the high priest: but after the death of the high priest the manslayer shall return into the land of his possession.