Caterpillar Inc. shares headed for the steepest decline in eight months as the world’s biggest maker of machinery for mining and construction had its offices raided by law enforcement officials. Searches were conducted Thursday in Peoria, East Peoria and Morton by the Internal Revenue Service, the Federal Deposit Insurance Corp. and the Commerce Department, Sharon Paul, a spokeswoman for the U.S. attorney’s office for the Central District of Illinois, said in by telephone.