Blair was a promising young reporter
A reporter with the highly respected New York Times committed repeated "acts of journalistic fraud", including stealing material from other papers and inventing quotes, the newspaper has admitted.
An internal review found problems in at least 36 of the 73 articles written by Jayson Blair, 27, from the time he got national reporting assignments last October to his resignation on 1 May.
Serious lapses were also found in random checks on the more than 600 articles he wrote over the rest of his four-year career at the New York Times.
Mr Blair repeatedly violated the cardinal tenet of journalism, which is simply truth
"The widespread fabrications and plagiarism represent a profound betrayal of trust and a low-point in the 152-year history of the newspaper", the New York Times writes in its Sunday edition.
The newspaper apologised to its readers and gave a detailed account of articles containing misleading information, false quotes and sentences lifted from other publications.
"In the final months the audacity of the deceptions grew by the week, suggestion the work of a troubled young man veering toward professional self-destruction," the paper says.
It cited several reasons for not detecting the problems, including "a failure of communication
among senior editors; few complaints from the subjects of (Mr Blair's) articles; his savviness and his ingenious ways of covering his tracks".
The review began in late April, after a Texas newspaper pointed to similarities between an article it had published and a story by Mr Blair.
The article was about a mother waiting for news of her son, a soldier missing in Iraq.
The subsequent investigation showed that while filing stories supposedly from around the country, Mr Blair had often not left New York.
Other instances of journalistic fraud include:
- In an article in October Mr Blair gave false details about a police interrogation of a man suspected of being the Washington sniper
- In March he wrote a piece about relatives of Private Jessica Lynch, a PoW rescued in Iraq - without ever visiting them
- In April Mr Blair described the scene at a Navy hospital in Maryland where soldiers were said to be recovering from serious wounds - an emotional story that was entirely spurious.
"Mr Blair repeatedly violated the cardinal tenet of journalism, which is simply truth," the New York Times writes.
The investigation into Mr Blair's work continues - especially on more than 600 articles he wrote before last October.
The revelation comes just days after another disgraced young journalist published a fictional account of how a reporter can resort to fabrications.
Stephen Glass was a rising star at The New Republic - a leading political magazine based in Washington - when the paper sacked him in 1998.
Dozens of stories he had written in the previous two years had turned out to contain false information and quotes.
Mr Glass later said he committed fraud out of a desire for recognition.
His book is a novel entitled The Fabulist.
In an author's note, Mr Glass writes that it is "inspired by certain events in my life".
"This book is a work of fiction, a fabrication, and this time, an admitted one."