At the lab, Carballo and his colleague, biological anthropologist Rebecca Storey, examine several bones.
This is an example of a burial found underneath an apartment compound in the Tlajinga district.
It's a male skeleton.
From the artifacts found with the remains, the scientists theorize that he may have been a leader of a neighborhood on the outskirts of the city.
But there's still more to learn from these bones.
He died in Teotihuacan.
But one of the interesting questions we have is where did he live?
Was he a Teotihuacano all his life?
And as it turns out as one of the most exciting things that's come up in skeletal analysis has been the ability to test where people lived as children and as teenagers.
And the secret is the teeth.
The teeth form from a time that you are a very small child up until you are an adolescent.
And as it turns out once the enamel has formed it is permanent, nothing changes.
The drinking water that you take up as a child and then gets incorporated into your enamel has different isotopic signatures depending on where you were geographically and climate wise.
And what you do is, you test the enamel of the teeth and you test the bone and you see if they are the same.
The results are stunning.
His teeth were tested and turned out to have a signature very different from Teotihuacan.
Isotope tests conducted on dozens of other remains all yield the same results.
With this information, Carballo and Storey conclude that tens of thousands of Teotihuacan's ordinary citizens came from other parts of Mesoamerica.
What that tells you is that they are migrants.