The unmasking of Isis militant "Jihadi John" as a Londoner who had repeatedly been questioned by security services has sent shock waves through Britain.
Prime Minister David Cameron has even stepped in to defend British spy craft.
Cameron tried to defuse criticism of Britain's intelligence community, which had the Isis executioner on its list of potential terror suspects for years but was unable to prevent him from travelling to Syria, where he has played a prominent role in grisly beheading videos.
Cameron did not mention "Jihadi John" or refer to his real identity: Mohammed Emwazi, a Kuwait-born computer science graduate raised and educated in Britain. But he said the country's spies make "incredibly difficult judgments" daily about how to pursue threats to national security and have broken up plots that would have caused immense damage.
Emwazi had been known to the British intelligence services since at least 2009, initially in connection with investigations into terrorism in Somalia.
David Anderson, who is in charge of reviewing Britain's terrorism legislation, said intelligence agencies may have dropped the ball, but faced a big challenge to identify real threats from "hundreds, probably thousands" of suspects.
The case has parallels to that of two al-Qaeda-inspired extremists who murdered a British soldier in a London street in May 2013. A report concluded that delays and other failings by the agencies had contributed to that tragedy.
However, it is not clear what laws could have been used to prevent Emwazi from leaving Britain then, since he had not been charged with any terrorist-related offences.
His identification as the front man in Isis murder videos has raised questions about how a soccer-playing London youngster who liked smart clothes became one of the world's most wanted men.
Authorities were working to piece together the path to radicalisation of Emwazi, who came to Britain from Kuwait as a child and studied computer science at the University of Westminster.
Court documents from 2011 obtained by the BBC list Emwazi as part of a network of West London men suspected by MI5 of sending funds, equipment and recruits to al-Shabaab militants in Somalia.
Emails that Emwazi sent to a Muslim advocacy group reveal a young man increasingly frustrated by the attentions of British spies and angry at the plight of Muslims around the world.
Emwazi approached the group Cage after he and two friends were arrested and deported on a trip to Tanzania in August 2009. The following year he accused British agents of preventing him from going to Kuwait, where he had a job and planned to marry. He seemed to feel that Muslims were under attack in many parts of the world and complained to Cage of the plight of his fellow believers in Chechnya, Iraq and elsewhere.
Meanwhile, a video of jihadists in Iraq gleefully smashing ancient statues with sledgehammers has sparked fears that more of the world's heritage will be destroyed.
The destruction of priceless Assyrian and other artefacts from the main museum and an archeological site in the northern city of Mosul drew comparisons with the 2001 dynamiting of the Bamiyan buddhas in Afghanistan.
Archaeologists and heritage experts called for urgent action to protect the remains of some of the oldest civilisations.
The head of the United Nations' cultural body Unesco, Irina Bokova, said the International Criminal Court should also take action.
Iraqi Prime Minister Haider al-Abadi called it a "provocation" to the world and warned Isis has destroyed several historical and cultural sites across Iraq, including Muslim shrines.
In the jihadists' extreme interpretation of Islam, statues, idols and shrines are a material corruption of the purity of the early Muslim faith and amount to recognising other objects of worship than God.
- AP, AFP