Pulitzer Prize-winning Washington Post reporter Sari Horwitz has been suspended for plagiarizing “substantial parts” of two recent news articles published by newspaper The Arizona Republic.

The Post reports that “Horwitz copied two paragraphs from a Republic story that described provisions of a federal civil rights law when she wrote an article that was first published on The Post’s website March 4. A second story, first appearing online on March 10, included 10 paragraphs from a Republic story about a search of Loughner’s home. Both stories appeared in the newspaper the day after they went up online.”

Both stories are now prefaced with this note: “This is one of two articles published by The Post online and in its print editions earlier this month that contained substantial material that was borrowed and duplicated, without attribution, from The Arizona Republic newspaper.”

The Post was alerted to the plagiarism by Republic editor Randy Lovely, and has since published Horwitz’s apology:

“I am deeply sorry. To our readers, my friends and colleagues, my editors, and to the paper I love, I want to apologize. … Under the pressure of tight deadlines, I did something I have never done in my entire career. I used another newspaper’s work as if it were my own. It was wrong. It was inexcusable. And it is one of the cardinal sins in journalism.”

The Post quotes its executive editor Marcus Brauchli:

“‘We [took] action that we think is appropriately severe and reflects the seriousness with which we view this transgression,’ Brauchli said in an interview. He said he had conducted a review of all of Horwitz’s published work this year and found no other evidence of plagiarism. Editors also saw nothing of concern when reviewing dozens of stories she wrote before this year, he said.”

In an editor’s note, The Post write “It is The Post’s policy that the use of material from other newspapers or sources must be properly attributed. The Post apologizes to the Arizona Republic and to its readers for this serious lapse.”