The battle in question is Battle of Puebla on 5th May 1862. Actually, many sources say that the number of French soldiers was 6,500 - so between 6 and 7 thousand! However, I think that the safer option is 6000 as many other sources say "just above 6000".
The FBI has traditionally been the lead federal agency in the response to and investigation of terrorism. Department of homeland security has the lead now.