ST. LOUIS (AP) — St. Louis Post-Dispatch columnist Tony Messenger has won a Pulitzer Prize for his series of columns about debtors' prisons in Missouri.

The Pulitzer winners were announced Monday. Messenger won in the category of commentary.

Messenger found defendants across Missouri who owed thousands of dollars in "board bills" for time spent in jail even though they had fulfilled their sentences or served out parole.

As a result of his work, the Missouri Supreme Court ruled that judges can't use courts to threaten indigent defendants with jail time, nor can they collect debts as court costs.

Post-Dispatch President and Publisher Ray Farris said Messenger's work "exemplifies the highest standards of our profession."

The newspaper also won a Pulitzer Prize, U.S. journalism's highest honor, in 2015 for photographic coverage of the unrest in Ferguson after Michael Brown's death.