Louisiana’s prison system routinely holds inmates for weeks or months after they were supposed to be released from custody following the completion of their sentences, the U.S. Justice Department said in a lawsuit filed Friday.

The lawsuit against the state comes after a multi-year investigation into a pattern of “systemic overdetention” that violates inmates’ rights and costs taxpayers millions of dollars per year.

Since at least 2012, more than a quarter of the inmates scheduled to be released from Louisiana prisons have been held past their release dates, according to the DOJ.

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The Justice Department warned Louisiana officials last year that it may file a lawsuit against the state if it failed to fix the problems. Lawyers for the department argue that the state made “marginal efforts” to address the issues, noting that such attempts at a fix were “inadequate” and showed a “deliberate indifference” to the constitutional rights of inmates.

“[T]he right to individual liberty includes the right to be released from incarceration on time after the term set by the court has ended,” Assistant Attorney General Kristen Clarke said in a statement.

“To incarcerate people indefinitely … not only intrudes on individual liberty, but also erodes public confidence in the fair and just application of our laws,” the statement added.

Louisiana Gov. Jeff Landry and state Attorney General Liz Murrill, both Republicans, attributed the problem to the “failed criminal justice reforms” pushed by “the past administration.”

“This past year, we have taken significant action to keep Louisianans safe and ensure those who commit the crime, also do the time,” Landry and Murrill said in a joint statement to The Associated Press. “The State of Louisiana is committed to preserving the constitutional rights of Louisiana citizens.”

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The two state officials also purported that the lawsuit is a last-ditch effort by President Biden, who leaves office next month, arguing that President-elect Trump’s incoming administration would not have pursued the case.

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Advocates have repeatedly challenged the conditions in Louisiana’s prison system, which includes Angola, the largest maximum-security prison in the nation, where inmates pick vegetables by hand on an 18,000-acre lot. The site was once the Angola Plantations, a slave plantation owned by Isaac Franklin and named after Angola, the country of origin for many of the enslaved people who worked there.

The Associated Press contributed to this report.