Updated 2:35 p.m.

CNN has fired a news editor in its London bureau for repeated plagiarism offenses, it announced in an editor’s note today.

An internal investigation at the network found that Marie-Louise Gumuchian had published about 50 stories containing plagiarized work. Those pieces contain a total of 128 separate instances of plagiarism, according to a CNN source, and the investigation is ongoing. Gumuchian covered international news, including Africa, Europe and the Middle East.

Most of the plagiarized material, notes the source, came from Reuters. (Gumuchian has an extensive archive of work at Reuters.) CNN says that it has removed the plagiarized work from Gumuchian’s pieces and, in some cases, deleted entire pieces from its Web site. “Trust, integrity and simply giving credit where it’s due are among the tenets of journalism we hold dear, and we regret that we published material that did not reflect those essential standards,” reads the editor’s note.

Here’s a noteworthy aspect of this case: CNN received no complaints about the plagiarism, according to a CNN source. Instead, it was discovered last Thursday in a routine editing check. From there, CNN ran the material through plagiarism-flagging software, according to the CNN source. That initial scan, says the source, turned up “two or three things,” which caused a deeper examination of “all of her work.” That uncovered an “insane” number of problems, according to the source.

CNN’s investigation, which called on the labor of around eight employees, may never have taken place if not for the work of a single copy editor, says another source at the network. There was something strange about a certain passage in one of Gumuchian’s stories, so the copy editor pumped it into Google. Up came a story from Reuters with the same passage. When Gumuchian was asked about the overlap, she said that she’d worked at Reuters for nine years and that it wouldn’t surprise her if she used language similar to that found in a Reuters piece. “She didn’t have much to say,” says the source.

When asked to characterize the plagiarism, the CNN source said that there were some passages with “artful twists” as well as a great deal of “background material” copied from elsewhere as a shortcut for the writer.

CNN’s editorial process caught the problem early: Gumuchian had been at the network only six months when the problems were exposed. That said, CNN is looking at ways to snuff out such problems earlier by “baking in” plagiarism checks even more routinely into the editing process. “Of course, we wish we would have caught it the very first time with an unpublished story,” says a CNN source. The filched copy shook Gumuchian’s colleagues: “We had good faith in her,” says a network source. “She had great recommendations, a great career at Reuters and she did extremely well in the interview process.”

CNN has advised Gumuchian’s previous employers of the problems, and it has placed this text on certain articles:

Editors’ Note: This article has been edited to remove plagiarized content after CNN discovered multiple instances of plagiarism by Marie-Louise Gumuchian, a former CNN news editor.

A Reuters spokesperson said Friday afternoon: “While employed by Reuters we were not aware of any concerns raised about Ms. Gamuchian’s work. However in light of press reports we are reviewing her stories.”