Complex sentence: Sandie N. Tillotson bought the top floor of the then uncompleted north tower for $30 million shortly after the September 11 attacks--a record for a condominium at the time.
Split into simpler sentences: Sandie N. Tillotson bought the top floor of the then uncompleted north tower for $30 million shortly after the September 11 attacks. It was a record for a condominium at the time.