You can search for the GMT+??, looking at the product in their apts and seeking on a search engine, listening to what they say and locating the regions lingo differences, watching tv with them and looking for that episode or movie to locate in which area it is aired, (music is easiest to locate an area or region)
look at the laptop and try to find out if any of the models are sold only in certain areas like here in America. If your on premium and you have some cameras looking outside, you could always try and find the location of these building and analyze your info if you find where.
They are so many techniques to investigate pictures, movies, cams etc... to find people.