An investigation led by Sen. Elizabeth Warren's (D-Mass.) office concluded that the accreditation process for prisons, jails and detention centers in the U.S. is rife with corruption and leads to little oversight of facilities.

Warren's staffers found in a report published by Mother Jones on Monday that just four facilities out of more than 1,200 operating nationwide have failed to qualify for accreditation with the American Correctional Association, a nongovernmental organization.

Facilities applying for accreditation are given months of notice ahead of routine audits as well as tools to help them pass, essentially guaranteeing continued accreditation by most detention centers, according to the investigation.

“A review of available evidence suggests that that accreditation has little to no correlation with detention facility conditions and practices, and therefore little to no value whatsoever,” reads the report, according to Mother Jones. “The result has been the rubber-stamping of dangerous facilities and the waste of millions of taxpayer dollars.”

The report notes the American Correctional Association is funded largely by private for-profit prison companies and serves as a lobbying arm for the industry on Capitol Hill. 

The organization denied that there is anything "nefarious" in helping facilities pass the auditing process, but added in response to Warren's report that it is also "considering" surprise inspections.

The industry has long been criticized by progressive lawmakers and advocates of criminal justice reform.

Officials in California moved to ban the state from contracting with for-profit prison companies last year, citing the industry's "practice of profiteering off the backs of Californians in custody." 

"Relying on a private organization to accredit and inspect private detention facilities that have a sub-par health and safety record is a recipe for disaster," Warren said in a statement last year announcing the investigation. "In industry after industry, outsourcing accountability has allowed corporations to evade standards with little to no consequences."