Forensic entomologists, of course.
These are the strong-stomached folks who study the arthropod fauna that colonizes dead flesh. Their knowledge of insect taxonomy, ecology, and development can be used to provide estimates of the time and conditions of death. Or zombification, in the present case.
Hypothetically, suppose a zombie shuffles along to my house at horrifying rate of 1 km/hr.
On arrival, I note that the zombie is infested with final instar larvae of the blow fly Phormia regina. Under our current warm summer weather conditions, it takes at least 5 days for the maggots to reach that developmental stage since momma fly visited the zombie. So we can presume that the zombie has been decomposing for at least that long.
Let’s see. 5 days is 120 hours. Shuffling at 1km/hour would put the origin of that zombie no further than 120 kilometers away.
If we collect maggots and crunch the numbers from enough zombies, we should be able to triangulate in on the location of the zombie epicenter. The zombie control forces will then be able to deploy where they will be most effective.
And as usual, entomologists will have saved civilization.
On a more personal note, though, I guess I should have run instead of doing the math.