They owned a piece of the investment trust that owned 75% of the building.
What the trust does is collect a bunch of money from a number of investors, and use that to buy the property. In this arrangement, you don't have a bank mortgage, the money that would go to the bank gets paid to the trust, and distributed to the investors. They can be good investments, a lot of what they pay out is tax sheltered income.
I used to do a lot of accounting for real estate investment operations, although not necessarily REIT's.