For more on the story - the plant is owned by Middle Easterners, one of the owners had his house in Chicago raided and other locations also were raided, and there are three nuclear plants nearby. As one comment said, “You don’t need 2 helicopters, 100 agents, Homeland Security, County police, and 30 squad cars for a couple undocumented workers.” The comments at links are eye openers.
http://www.newstin.com/rel/us/en-010-019287057
http://www.chicagobreakingnews.com/2009/10/fbi-raid-chicago-mans-home-meat-packing-business.html
http://www.morrisdailyherald.com/articles/2009/10/19/98658403/index.xml
From one of your links...
"Basically, all the FBI can say is its a very sensitive criminal investigation thats ongoing,"
As you point out, rounding up Mexicans for deportation is never described as "a very sensitive criminal investigation".
* The name of the plant in the Grundy County town of Kinsman, IL is "First World Management"
* The owner's residence which was also raided is in Chicago in the 6000 block of North Campbell Avenue.
* At least two other Chicago locations were also raided.