OMAHA, Nebraska — A large federal law enforcement operation conducted Wednesday targeted businesses in Nebraska and Minnesota that officials say knowingly hired — and mistreated — immigrants who are in the U.S. illegally. The investigative arm of U.S. Immigrations and Customs Enforcement — Homeland Security Investigations — led the operation that saw about a dozen businesses and plants raided and 17 business owners and managers indicted for fraud, wire fraud and money laundering. Of those, 14 were taken into custody Wednesday and three were still being sought.