Although I suppose it is possible they could suspect you and find your new location and monitor you from there. I just think it is less likely that the police will trace to a dead end at open WiFi and then try to determine everybody who lived around the area at the time the session of interest was identified, put them all under surveillance, etc. For all they know it could have been somebody war driving. In cases where the police trace criminal activity to a open WiFi hotspot these days they do analyze the wireless spectrum around the hotspot trying to see who all is using the open wireless network and trying to continue their trace of the suspect they are trying to identify, but I think in most cases where this fails they close the case as there are too many possibilities of what could have happened. It could be a neighbor who still lives in the area who no longer engages in the pattern of criminal activity, it could be somebody who went war driving, it could be somebody who moved away after the last session was identified, etc. In many cases that significantly increases the complexity of continuing the investigation, especially if it is in an area with many apartments where people come and go regularly. Now over time and multiple trace backs to the same location they can start to do more interesting things, and over multiple trace backs to multiple locations they can do even more interesting things (in either case intersection attacks are the first thing that comes to mind), and we have seen the FBI do this in at least one high profile case (with the WiFi being used at hotels), but in the end it still adds complexity to their investigation and in some cases it may make it impossible for them to identify their suspect, so it is definitely better than using your own internet I would say. I wouldn't put all of my eggs in the WiFi basket, it makes it technical trace more difficult but there are all kinds of intersection attack possibilities over time. Somebody who war drives may never be traced back with a live trace, but if they live in a city with license plate scanners and they have two sessions traced back to the hotspot they used an intersection attack of license plate numbers scanned in a radius around the access points in the time around when the sessions were identified would probably be enough to identify their car, for example. And if you use WiFi at hotels, even if they do not get you with a live trace they can do intersection of people who were registered at those hotels during the times the sessions were identified. But in either case it is still arguably better than having them trace directly to your IP address, and in some cases it could bring you from being traceable to untraceable.