Federal investigators have found that Sen. Joe Lieberman’s re-election campaign caused its Web site to crash on the eve of the August 2006 primary, a collapse he had blamed on supporters of Democratic challenger Ned Lamont.

“In short, the server that hosted the joe2006.com Web site failed because it was overutilized and misconfigured,” according to an Oct. 25, 2006, e-mail included in FBI documents obtained Wednesday by The Associated Press. “There was no evidence of (an) attack.”

Investigators added that, once reported by the media, the accusations by Lieberman’s campaign helped overwhelm the Web site on primary day, too.

The Advocate of Stamford, Conn., first reported the results of the investigation.

Lamont said Wednesday that Lieberman should apologize.

“Senator Lieberman’s campaign team accused an awful lot of good people of breaking the law on the eve of the primary, and they did it for political purposes,” Lamont told the AP in a telephone interview. “If he does the right thing, he’ll stand up and say, ‘I was wrong.”

Lieberman had implied that Lamont supporters had hacked the site, saying on primary day: “I’m concerned that our Web site is knocked out on the day of the primary, you’d assume it wasn’t any casual observer.”

His campaign asked the Justice Department to investigate; Lamont’s campaign denied involvement.

A Lieberman spokesman said Wednesday that the Democratic-leaning independent senator considered the case closed.

“We were told by our Web site administrator that there was clear evidence of an outside effort to disrupt our site, and that the administrator was so certain that the site had been attacked that he was willing to swear to it in a legal affidavit,” Dan Gerstein said.

After a surprising loss to Lamont, a political newcomer, in the primary, Lieberman defied Democratic leaders and ran as an independent in the general election. Top Democrats backed Lamont and Lieberman won support from the GOP, including praise from the White House and fundraising help from prominent Republicans such as New York Mayor Michael Bloomberg.

Lieberman was Democrat Al Gore’s running mate in 2000, and he unsuccessfully sought the Democratic presidential nomination in 2004.

An independent who caucuses with Senate Democrats, Lieberman has emerged as one of Republican presidential candidate John McCain’s strongest supporters.

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Associated Press writer Lara Jakes Jordan contributed to this report.