You say that it looks like a Chaco? How big is it, approximately? Chaco tortoises are pretty rare in collections. They stay fairly small. On the other hand, Sulcatta tortoises are very common. They look a lot like a Chaco, but are usually more than twice the size.

A good identification site is www.chelonia.org..."species galleries"..."galleries by genus"...look at "Geochelone", "Gopherus", "Manouria", and "Testudo". Individuals in any of these genera can sometimes look like a Chaco. If you narrow it down to a few species, do a google image search of the common name and also the latin name. Look for structural commonalities. Color can be misleading.

Good luck. Let us know what you think.