One likely scenario is police had listening devices in both his vehicle and home and knew his every little move.
Much like the analysis of the suspect's phone movements would have helped narrow him down as a suspect, so to would it have helped police track his movements.
I know this is off topic, it relates to the 2 elderly campers missing two years ago. The reason I am posting this is because PERHAPS Police used analysis of the FP phone movements to be able to narrow down the dig sites they are currently working on in Kendall. I can post a link but it is off topic but just trying to show a relationship in phone tracking abilities.