Court papers show Maricopa County Sheriff's deputies knew in August that more than 20 custodians contracted with the City of Mesa were using fraudulent information to illegally work in the United States but held off on arresting the Management Cleaning Control employees until last week, The Arizona Republic reports.

The documents, which led Maricopa County Superior Court Judge Gary Donahoe to issue a search warrant last week, shed light on the five-month fraud and ID-theft investigation that culminated when 60 deputies and posse members raided Mesa municipal buildings Thursday.

The court documents show that a City of Mesa employee raised the illegal immigrant issue with Mesa Police Lt. Wade Pew on May 20.

Unsatisfied with the Pew's response, the employee placed a phone call the next day to the sheriff's office and offered specific information about custodial workers using false IDs and Social Security numbers.
Mesa police announced Monday that they're conducting an internal investigation to determine if Pew violated any of the agency's procedures in his handling of the allegations.

Maricopa County Sheriff Joe Arpaio said last week that Pew's response to the situation was indicative of the Mesa Police Department's approach to fighting illegal immigration.