JACKSON, Miss. — Six of seven Mississippi chicken processing plants raided Wednesday were “willfully and unlawfully” employing people who lacked authorization to work in the United States, including workers wearing electronic monitoring bracelets for previous immigration violations, according to unsealed court documents.

Federal investigators behind the biggest immigration raid in a decade relied on confidential informants inside the plants in addition to data from the monitoring bracelets to help make their case, according to the documents. The sworn statements supported the search warrants that led a judge to authorize Wednesday’s raids and give a detailed look at the evidence in what Immigration and Customs Enforcement officials say is a yearlong investigation.

Officials arrested 680 people during Wednesday’s operation. Three Democratic congressmen on Friday demanded that the Department of Homeland Security and the Department of Justice produce information about the cost of the raids, whether employers face charges, whether any U.S. citizens were detained, and how many parents were separated from children.

The statements unsealed Thursday allege that managers at two processing plants owned by the same Chinese man actively participated in fraud and that supervisors at other plants at least turned a blind eye to evidence suggesting job applicants were using fraudulent documents and bogus Social Security numbers.

The documents say electronic monitoring bracelets show people arrested for immigration violations and not allowed to work in the U.S. were working at all seven plants. There have historically been few convictions for hiring people without documents because prosecutors must prove employers knowingly hired them. Employers often say they were fooled by fraudulent documents.