Complex sentence: The owner is hoping to obtain a tenant, possibly for retail, before any further investments are undertaken, which has left the building thus far 15 years without any occupancy and internally disfigured since Weinstein's ownership.
Split into simpler sentences: The owner is hoping to obtain a tenant, possibly for retail, before any further investments are undertaken. This has left the building thus far 15 years without any occupancy and internally disfigured since Weinstein's ownership.