When you purchase the property subject to an existing loan, the original borrower is not released from liability. As the purchaser you will assume the payments and hopefully make them on time as required. Should the loan become delinquent, the original borrower is named in any action or subsequent foreclosure. Should you purchase the property subject to a mortgage, and the person from whom you purchased it had done the same, the original borrower at the beginning of the chain is still liable.

