Employers use credit report before hiring

Half of the employers in the US use credit checks when making a hiring decision. They ask a company specialised on it to edit a credit report on an applicant, it's relatively inexpensive, between $20 et $50. Anyway some jobs as teachers, police officers, firefighters, require a credit check by law.
But why, even if it's not required by law, employers look for it ? It is suppose to give an indication about the integrity and the sense of responsability of the applicant. For some unemployed people, they are facing a vicious circle, they found no job because of it and money is so scarce, they have to take more loans... That's why some states ban this practice of credit screening.
Nonetheless psychology research papers found no link between a person's credit score and a "deviant" behavior like workplace theft.