Important documents such as the property deed, mortgage agreement, or liens are usually recorded with the county clerk.
If you are press for time you are welcome to go NYC Department of Fiance website, then click on ACRIS property records. If you know the property's information, you should be able to pull up the required information. Good luck on your endeavors.
Top That Realty Service L.L.C.
Licensed Real Estate Broker
The mortgage document or note may have a legal way for you to take possession of the property with the homeowner's blessing.
Larry Kennedy, Realtor