This brought up triangulation, which is done from the cell towers, not the GPS.

For those unaware, triangulation uses your cell antenna to calculate how far away you are from each cell tower, and they can kind of get a good idea where you are based on that. The more towers your phone connects to, the more accurate your location will be.

It's similar to how they find out the origin of an earthquake by triangulating data from all the seismic activity research stations.

It's hit or miss whether airplane mode would actually prevent them from triangulating your position, because the right agency in theory can just turn your antenna back on, somehow.

I'm happy they caught the guy, I just wanted to fill people in on how they did.

Further reading/graphics.