How do you get the internal id from search results?

Use case: I want to search for a specific customer using the nlapiSearchRecord() function, so that I can obtain the internal id for that custoemr and set the company field within a case record.

I can use nlapiSearchRecord() to retrieve the correct record, but how do I get its internal id? I'm assuming that a customer search returns a standard array of custoemr records. According to the reference guide, there is no internal id field for the customer. Is there another way to accomplish the use case above?

 var filters = new Array();  filters[0] = new nlobjSearchFilter('email', null, 'contains', 'test@test.com