The Massachusetts senator told FOX News' senior correspondent Geraldo Rivera that he believes he lost because the tape may have scared the American electorate.
Rivera spoke to Kerry on Thursday as the senator and a slew of other notable names — including wife Teresa Heinz Kerry, actors Robin Williams and Morgan Freeman and comedian Chris Tucker — were in a holding room prior to the processional leading up to the formal opening of the Clinton Presidential Library in Little Rock, Ark.
"Tough luck, senator," Rivera said to Kerry, referring to the Democrat's election loss.
Trying to recount Kerry's words verbatim, Rivera said Kerry responded by saying:
"It was that Usama tape — it scared them [the American people]."
Rivera said Kerry said the tape came out too late for his camp to rebut and the Democratic campaign couldn't counteract it in time for the Tuesday election.
"Sen. Kerry clearly believes not only is it the security issue that cost him the election, but very specifically the Usama tapes coming out in the 11th hour," Rivera reported Friday.
Kerry also acknowledged that the security issue in general hurt him in the race, Rivera said.
The broadcast of the tape from the Al Qaeda leader jolted the campaign's closing days, accentuating the terrorism theme with a reminder of the Sept. 11, 2001, attacks.
In the tape, aired by the Arab television network Al-Jazeera, bin Laden spoke directly to the American people. He admitted for the first time that he carried out the Sept. 11 attacks and said the attacks would have been less severe if Bush had been more alert.
He promised to lay out "the best way to avoid another Manhattan" and told Americans, "Your security is not in the hands of Kerry or Bush or Al Qaeda. Your security is in your own hands."
The tape caused Kerry to revive his contention that Bush missed an opportunity to capture or kill bin Laden during the Afghan war. The Democratic challenger asserted throughout the campaign that U.S. forces could have run down bin Laden in the Tora Bora (search) mountains in late 2001 if they had gone after him on the ground, and he blamed Bush for the decision to let Afghan forces lead that chase.
But during the campaign, Republicans insinuated that terrorists would prefer to see Kerry in office, saying the Massachusetts senator would be too soft in the War on Terror.
Some political observers believe that many Americans voted for Bush not only because of his strong stance in the War on Terror but because they held tight to the adage of, "you don't change horses in midstream."
House Minority Leader Nancy Pelosi, in responding to the FOX News report, said she does believe the bin Laden tape favored the president a little but would not say it outright tipped the election.
"It was a reminder he [bin Laden] still at large," she told FOX News. "I think what we could see in the polls a real lead for Kerry and that made a couple points difference … I think it had an effect."
On another note, Kerry is thanking supporters in an e-mail for moving voters, holding Bush accountable and for helping counter "the attacks from big news organizations" such as FOX News.
"I want to thank you personally for what you did in the election — you rewrote the book on grassroots politics, taking control of campaigns away from big donors. No campaign will ever be the same," Kerry wrote. "You moved voters, helped hold George Bush accountable, and countered the attacks from big news organizations such as Fox, Sinclair Broadcasting, and conservative talk radio."
Kerry went on saying the Bush administration is planning "a right wing assault on values and ideals we hold most deeply" and that diverse opinions are being "eliminated" from the State Department and CIA with the personnel reshuffling, and the Bush Cabinet is being remade to "rubber stamp policies that will undermine Social Security, balloon the deficit, avoid real reforms in health care and education, weaken homeland security, and walk away from critical allies around the world."
Kerry also vowed to "continue to challenge this administration" on a variety of issues, ranging from election standards and health care for children.
FOX News' Carl Cameron, Jim Mills, Liza Porteus and Geraldo Rivera contributed to this report.