Scotland Yard evidence room:treasure-trove of evidence: 11,000 pages of handwritten notes listing nearly 4,000 celebrities, politicians, sports stars, police officials and crime victims whose phones may have been hacked by The News of the World

For nearly four years they lay piled in a Scotland Yard evidence room, six overstuffed plastic bags gathering dust and little else.

Inside was a treasure-trove of evidence: 11,000 pages of handwritten notes listing nearly 4,000 celebrities, politicians, sports stars, police officials and crime victims whose phones may have been hacked by The News of the World, a now defunct British tabloid newspaper.

Yet from August 2006, when the items were seized, until the autumn of 2010, no one at the Metropolitan Police Service, commonly referred to as Scotland Yard, bothered to sort through all the material and catalog every page, said former and current senior police officials.

During that same time, senior Scotland Yard officials assured Parliament, judges, lawyers, potential hacking victims, the news media and the public that there was no evidence of widespread hacking by the tabloid. They steadfastly maintained that their original inquiry, which led to the conviction of one reporter and one private investigator, had put an end to what they called an isolated incident.

After the past week, that assertion has been reduced to tatters, torn apart by a spectacular avalanche of contradictory evidence, admissions by News International executives that hacking was more widespread, and a reversal by police officials who now admit to mishandling the case.

Assistant Commissioner John Yates of the Metropolitan Police Service publicly acknowledged that he had not actually gone through the evidence. “I’m not going to go down and look at bin bags,” Mr. Yates said, using the British term for trash bags.

At best, former Scotland Yard senior officers acknowledged in interviews, the police have been lazy, incompetent and too cozy with the people they should have regarded as suspects. At worst, they said, some officers might be guilty of crimes themselves.

“It’s embarrassing, and it’s tragic,” said a retired Scotland Yard veteran. “This has badly damaged the reputation of a really good investigative organization. And there is a major crisis now in the leadership of the Yard.”

The testimony and evidence that emerged last week, as well as interviews with current and former officials, indicate that the police agency and News International, the British subsidiary of Rupert Murdoch’s News Corporation and the publisher of The News of the World, became so intertwined that they wound up sharing the goal of containing the investigation.

Members of Parliament said in interviews that they were troubled by a “revolving door” between the police and News International, which included a former top editor at The News of the World at the time of the hacking who went on to work as a media strategist for Scotland Yard.

On Friday, The New York Times learned that the former editor, Neil Wallis, was reporting back to News International while he was working for the police on the hacking case.

Executives and others at the company also enjoyed close social ties to Scotland Yard’s top officials. Since the hacking scandal began in 2006, Mr. Yates and others regularly dined with editors from News International papers, records show. Sir Paul Stephenson, the police commissioner, met for meals 18 times with company executives and editors during the investigation, including on eight occasions with Mr. Wallis while he was still working at The News of the World.

Senior police officials declined several requests to be interviewed for this article.

The police have continually asserted that the original investigation was limited because the counterterrorism unit, which was in charge of the case, was preoccupied with more pressing demands. At the parliamentary committee hearing last week, the three officials said they were working on 70 terrorist investigations.

Yet the Metropolitan Police unit that deals with special crimes, and which had more resources and time available, could have taken over the case, said four former senior investigators. One said it was “utter nonsense” to argue that the department did not have enough resources.

Another senior investigator said officials saw the inquiry as being in “safe hands” at the counterterrorism unit.