A one-legged poison expert from Jordan could be the brutal new star of Islamic terrorism.
The man in question - Abu Musab al-Zarqawi - isn't yet the equal of Osama bin Laden, say experts. But he may be fast gaining influence and importance in the loosely organized world of Islamic militants by orchestrating attacks aimed at the US presence in Iraq.
Intelligence officials now say that Mr. Zarqawi was indeed the lead perpetrator of the murder of American businessman Nicholas Berg.
"After the intelligence agency conducted a technical analysis of the video posted on the Internet on May 11, we have determined - with high probability - that the speaker on the tape is that of Abu Musab Al Zarqawi, and that he is the person shown decapitating American Nicholas Berg," says a CIA official.
Zarqawi has also claimed responsibility for bomb attacks on the UN headquarters in Baghdad and an Italian police station in Nasiriyah, among others.
If nothing else, his rise to prominence shows how a new generation of terrorist leaders may be stepping in to replace those eliminated by US efforts.
"He has a long reach ... I'm sure [Zarqawi] has supporters scattered around the globe who would support his efforts if need be," says a US government official.
Establishing responsibility for terrorist attacks is an extraordinarily difficult intelligence task. Many times masterminds prefer to stay in the shadows, for obvious reasons. Groups or individuals sometimes claim credit for things they didn't do, in an attempt to puff their reputations and gain money and recruits.
Some experts believe the US may be exaggerating Zarqawi's role in Iraq in an attempt to more closely link the US presence there with a war on terrorism.
That said, Zarqawi, or someone purporting to be him, has issued a series of audio and video tapes in recent months that claim responsibility for a wide range of horrific actions.
In one 33-minute tape he called on Sunni Muslims to "burn the earth" under Americans' feet. In others he boasted that he was behind some of the worst bombings in Iraq since the US took control of the country last year.
On Tuesday, an Islamic website released a video it said showed Zarqawi personally killing Mr. Berg, a young Pennsylvanian who had traveled to Iraq in search of work constructing communications towers.
Abu Musab al-Zarqawi's real name is Ahmad Fadil al-Khalaylah. He takes his nom de guerre from the Jordanian town of Zarqa, where Palestinian terrorists blew up three hijacked airliners in 1970 in a pioneering act of anti-Western violence.
Zarqawi first appeared on the radar screens of Western intelligence agencies in 1999, when Jordanian authorities tied him to an aborted plot to blow up a tourist hotel in Amman during millenium celebrations.
Zarqawi, the son of wealthy Jordanian landowner, escaped to Afghanistan. There he ran an Al Qaeda training camp that specialized in chemical and biological agents, according to US intelligence.
Wounded in the leg during a bombing raid in the Afghan war in 2001, he ended up in Iraq, where doctors reportedly fitted him with a prosthetic limb.
US intelligence subsequently tracked him around the Middle East. Among known contacts is a meeting with Hizbullah leaders in south Lebanon in August 2002.
In October 2002, two gunmen assassinated US diplomat Lawrence Foley in Jordan. Caught, the gunmen fingered Zarqawi as the mastermind of the plot. For this, last month he was sentenced to death in absentia in Jordan.
Zarqawi's decentralized network is known as Al Tawhid. In the past, one of his main avowed goals has been to topple the Jordanian royal family.
That probably remains one of his aims, say terrorist experts. But they add that he seems to have expanded his operations with the advent of the US war on terror.
"Zarqawi is building a state-of-the-art operational and support network beyond the Middle East into Europe and North America," says Rohan Gunaratna, a terrorism expert based in Singapore, and author of "Inside Al Qaeda. "He works with about a dozen other Islamist groups ... Al Ansar Al Islami [and] Al Qaeda among them."
But Zarqawi is both an ally and competitor of these groups, according to the testimony of a captured follower. He vies with the better-known network of Osama bin Laden for contributions from the faithful, credit for attacks, and even for prized terrorist recruits.
With the advent of the US wars in the region, he appears to have shifted his aims and moved his base of operations inside Iraq itself.
In terms of terror prominence, Zarqawi "would be No. 1 in Iraq, but Osama bin Laden is still No. 1 overall," says a US government official who spoke on condition of anonymity.
In recognition of the danger he poses, the US has promised a reward of at least $5 million for information leading to Zarqawi's death or capture.
Not everyone in the intelligence community, however, agrees that Zarqawi is behind the beheading of Berg.
"We don't think he is behind this decapitation," says a European intelligence official. "He is more sophisticated than that."
In fact, the intelligence official from that country, a partner with the US in the war on terror, refers to Zarqawi as a "gentleman terrorist" because of his predilection for the use of poisons over more brutal methods.