FOR most people the videotaped execution of Nicholas Berg was a graphic reminder of the risks involved in waging war on a violent terrorist enemy. For others, however, it was evidence of a conspiracy.

Take, for example, the suspiciously white ear that appears shortly after frame 9,306 of the beheading video. It appears to belong to a captor wearing an American cap.

Quite why an Islamic terrorist would be wearing an emblem of the enemy has yet to be explained. This is one of at least 50 anomalies now being pored over by video experts, computer analysts and internet surfers.

The arrest last week of four Iraqis suspected of involvement in the revenge killing of the 26-year-old civilian adventurer has added to the confusion, fuelling doubts about official accounts of Berg’s visit to Iraq.

Moreover, it has refocused attention on the bizarre sequence of coincidences and contradictions that led to his death. His past links to an Al-Qaeda terrorist have raised questions in some quarters as to whether he might even have been working for the intelligence services.

Wandering across Iraq in search of business for Prometheus Methods, his fledgling Pennsylvania-based communications company, Berg would introduce himself in halting Arabic as “the tower guy”. He specialised in climbing radio and mobile phone installations to inspect, repair and upgrade them.

There was nothing in the young American’s e-mails home to indicate any sinister connections. He even laughed off a 13-day spell in jail after Iraqi guards spotted an Israeli stamp in his passport — a serious faux pas in the Arab world.

Six weeks ago he checked out of his Baghdad hotel and told the receptionist: “Inshallah (God willing) I will be back in a few days.” His body was found on May 8 on a Baghdad motorway overpass, but it was not until three days later that his family learnt how he died.

The video posted on the Muntada al-Ansar site claimed that Berg had been killed in revenge for the US abuse of prisoners at Baghdad’s Abu Ghraib jail. The CIA later announced that it believed the man who read a statement and then wielded the knife was Abu Musab al-Zarqawi, a Jordanian Islamic militant with ties to Osama Bin Laden.

As America recoiled in horror at descriptions of the blood-curdling murder, Berg’s family disclosed a curious connection. Five years earlier, Berg had attended the University of Oklahoma. At a nearby flight school at the same time, an Islamic militant named Zacarias Moussaoui was taking pilot lessons. Moussaoui, a French Moroccan, is awaiting trial on charges that he would have been one of the September 11 hijackers had he not been arrested beforehand.

When the FBI began examining Moussaoui’s local links it made an extraordinary discovery. He had been using Berg’s university e-mail password.

Michael Berg, Nicholas’s father, has said his son innocently gave his password to a man he met on a bus. The man is believed to have been Hussein al-Attas, a student at an Oklahoma community college who had become friendly with Moussaoui and who asked if he could borrow Berg’s laptop computer to send an e-mail home. Al-Attas is now in US detention.

When Berg was arrested at a roadblock in Mosul, northern Iraq, last March, his Moussaoui connection provoked further scrutiny of the password incident. He was interrogated three times by FBI agents in Mosul.

Eventually he was released, and a Justice Department official insisted last week that however unsettling it seemed that a civilian randomly executed by Al-Qaeda should himself have been investigated for Al-Qaeda links, officials had no doubt it was “a total coincidence”.

The plot seemed to thicken when Michael Berg’s grief at his son’s murder turned to rage against the US administration. Berg claimed that his son’s detention in Mosul had been unlawful, and had “immersed my son in a world of escalated violence . . . were it not for his detention (I) would have had him in my arms again”.

This improbable sequence of events provoked intensive scrutiny of both the US government’s treatment of Berg and the video that shows his death. While some of the anomalies appear easily explained by the obvious editing of the tape, others have excited intense debate.

The CIA’s insistence that al-Zarqawi was responsible appears based on the scantiest of evidence. Al-Zarqawi is known to have lost one leg, yet there is no sign on the video of either a prosthesis or any awkward movement. Sound experts have speculated that the voice might have been dubbed on.

Other questions have been raised about the orange jumpsuit worn by Berg, which appears similar to those worn by prisoners at Guantanamo Bay. He is sitting on a white chair, similar to one shown in an image from Abu Ghraib prison. There are discrepancies in the times on the video frames.

No credible motive has yet been advanced for the suggestion among conspiracy theorists that US forces might have faked a video to cover up Berg’s death. More problematic is the government’s claim that al-Zarqawi was responsible.

Two of the four Iraqis arrested in connection with Berg’s murder have already been released. The others are believed to be former members of Saddam Hussein’s Fedayeen militia, and might have been loyal to Yasser al-Sabawi, a nephew of Saddam who continues to fight coalition forces.

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