Intelligence officials conducted a technical analysis of the video released on an Islamic web site and determined "with high probability" that the person shown speaking on the tape — wearing a head scarf and a ski mask — is al-Zarqawi, a CIA official said, speaking on the condition of anonymity.
The speaker — determined to be al-Zarqawi — is then shown on the video decapitating American citizen Nicholas Berg, the official said.
Berg's body was found in Baghdad on Saturday. On Tuesday, an Islamic Web site released the video, titled "Sheikh Abu Musab al-Zarqawi slaughters an American infidel with his own hands."
The speaker on the video reads a lengthy statement criticizing Islamic scholars and taunting the crusaders.
Standing alongside four other militants wearing headscarves and masks to disguise themselves, al-Zarqawi then kills Berg.
Berg's death was reminiscent of the 2002 killing of Wall Street Journal reporter Daniel Pearl, who also was decapitated while a video camera captured the execution.
Like Berg, Pearl's killing was initially thought to have been handled by underling, but was later determined to be done by Khalid Shaikh Mohammed, a senior al-Qaida operative and alleged mastermind of the Sept. 11 attacks.
Al-Zarqawi is thought to be in Iraq, operating his own terrorist network, known simply as the "Zarqawi network." A specialist in poisons, he is thought to have extensive ties across the militant Islamic movement and is considered an ally of Osama bin Laden.
As recently as March, U.S. officials said al-Zarqawi's practice was not to make taped public pronouncements or take credit for attacks. However, in the last five weeks, he has increased his public profile with at least three recordings, including Berg's beheading.
Al-Zarqawi is also believed to be behind well over a dozen high-profile attacks in Iraq, and many other acts of violence, which have killed hundreds.
The United States is offering a $10 million reward for information leading to his death or capture.