Most journalists spend their time trying to make cracking stories out of a world that’s mundane, where quotes are inelegantly phrased and the truth is complex. The temptation to fabricate, fudge or plagiarise in pursuit of the killer quote is always there, but the consequences of being caught are career-ending.

Overnight in America, Guardian US editor Lee Glendinning published a note to readers “about a reporter who breached our trust”.

“We’ve published this because The Guardian aims for the utmost transparency with our readership,” she wrote on Twitter. “I want Guardian readers to know how disheartened I am to publish such a note.”

The note revealed that The Guardian had recently commissioned an “independent fact-checker” to research 37 articles and 20 opinion pieces it had published in 2015 and 2016 by Joseph Mayton, after being contacted by “sources” who claimed they had not spoken to Mayton but were quoted in his pieces.

This investigator:

“… found articles that contained likely or confirmed fabrication, including stories about two events that organisers said he didn’t attend. Dozens of sources could not be found — either they had no online presence or they were anonymous and could not be substantiated – and several people quoted in Mayton’s articles either denied speaking with him or giving the quotes attributed to them.”

The piece says The Guardian met with Mayton twice to discus the allegations and emailed him “dozens of times” over a month to seek further information, “but he was unable or unwilling to provide information on most sources”.

Given this, The Guardian has removed 12 of Mayton’s articles and one opinion piece, and removed quotes and information its investigator couldn’t verify from many others.

The case, Glendinning’s note says, shows the difficulties publications face in how they deal with freelancers:

“Mayton wrote only sporadically for the Guardian — he was an infrequent but long term contributor and many different editors in the organization have dealt with his work across opinion, news, arts, sports and features. At first, the quality of his writing met our standards, and thus a trusted working relationship was established.”

The Guardian will now find out more about about freelancers before trusting them, the note concludes.

But Mayton, who The Guardian said hadn’t provided any on-the-record comment about the Guardian’s investigation, posted a statement after the piece went up in which he also agrees the episode has lessons for freelancers. But rather different ones than The Guardian believes.

He rejects The Guardian’s “false accusations”. He says he may have been sloppy with record-keeping — a mistake freelancers should not make — but says he never fabricated anything.

“I have provided evidence showing that many sources had in fact spoken with me and either did not remember or refused to be truthful,” he wrote, adding that he’d provided The Guardian with his phone records. But given many of the interviews occurs months or years past, it was hard to now confirm the quotes were accurate.

“My notes are gone as I did not keep them or they have been lost, which sadly, included the interviews and contact information. Obviously, that was my mistake and my responsibility. If the Guardian had asked for those earlier or requested more information when articles went live (or before), I could have provided it easily, as I have always worked with editors and any request, including contact information and sources’ full names as they were given to me.”

Freelancers, Mayton writes, are “sometimes expendable”:

“If a top company with weight claims something, a freelancer better have all details required. I have given all the available evidence that I can now give to the Guardian, but the sources appear to have gone back on what they said to me.  …

“Sometimes, sources go back on their statements and the only way to prove what they said is with an audio recording, which I failed to do, and because the freelancer only has their word, they are the ones who will be scapegoated, as I feel this is the case here.”