Last summer, senior News International officials said that in that crucial period in 2008, Mr. Murdoch had neither been told about nor shown documentation of the extent of the illegality at The News of the World. The discovery of the e-mail, said one former official with knowledge of the situation, was completely unexpected.

Why did it take so long to come to light? Linklaters, a law firm working for News International, said that a junior employee found it in November, but that senior officials at the firm did not know about it until December.

In addition, Linklaters told the Commons Committee on Culture, Media and Sport, Mr. Myler’s electronic copy had been lost “in a hardware failure” on March 18, 2010,” while Mr. Murdoch’s electronic copy had been deleted on Jan. 15, 2011 during an “e-mail stabilization and modernization program.”

Big corporations routinely delete old e-mails. Between April 2010 and July 2011, News International discussed e-mail deletion with HCL Technologies, which manages its e-mail system, on nine occasions, according to a letter HCL wrote to Parliament last summer.

Most of the reasons were mundane. But in January 2011, HCL said, News International asked whether HCL was capable of helping “truncate” — meaning delete — “a particular database” in the e-mail system. The question came shortly after disclosures in a civil suit brought by the actress Sienna Miller raised fears that material about widespread phone hacking at The News of the World might become public.

News International did not explain why it wanted the deletion. HCL said it could not help and told the company to look elsewhere.

It is not clear whether the “stabilization and modernization program” that deleted the Murdoch e-mail was linked to News International’s request to “truncate” data. But it is clear that on Jan. 15, when the deletion took place, the company knew it was facing civil and potentially criminal inquiries. A month earlier, reacting to new information from the Miller and other cases, it had suspended the News of the World’s news editor, Ian Edmondson, on suspicion of phone hacking, and handed some material to the police.