Property ownership is public record: http://www.hcad.org/Records/Real.asp#Addr You have to play around with the street name quite a bit to get it to work. I had to type in just the first four letters of the street to find a few of the ones I knew about. Call up the landlord and tell him/her that you are an old high school friend of ________ and you need to call them because someone in your old circle of friends passed away yesterday and the funeral is on Thursday. This was the last place that she lived when you were still in touch and you don't know where to turn.
forgot.... if they have only moved once since then, it might be possible to get the forwarding address since they probably have it for sending the deposit check back.