We know who robbed the bank, it was clearly the bank robbers!

Archeology is my fav.

It was a carefully planned large city with the road along the main axis pointed at 15 degrees east of north, and the large pyramids were integrated into the city's design, but we definitely don't know who did that planning. Hundreds of apartment compounds were standardized. Tens of cubic meters of earth were moved and they had to quarry lots of basalt and other stone.

There is strong evidence it was a multi-ethnic city, especially since there are distinct ethnic neighborhoods based on artifacts such as pottery. No trace of writing or how the city and government were organized, and whether a ruling elite called the shots or if there were ruling families from different ethnic groups working together.

This feels kind of tautological. We know who built Teotihuacan, it was the Teotihuacanos! What do we know about them? Well, they built Teotihuacan...

(Seriously, though, _is_ anything much known about them beyond that?)