Most of the European recruits to Islamist terrorism, say security experts, are well-educated and are potentially successful people.
Bernard Squarcini, head of the French internal security service, told Le Monde newspaper: "He (Merah) resembles no other pattern we have seen until now... What he did points more to a mixture of medical problems and fanaticism than the usual career of a jihadist."
According to the transcript of his siege conversations, Merah said that he wanted to "have the honour of dying with a gun in my hand like a mujaheddin."
A post-mortem found his body was "riddled" with police bullets when he resisted arrest last Thursday. Initially, the authorities had spoken of a single sniper shot to the head.
But despite apparently professing grand aspirations, a police source who leaked short extracts of Merhat's "confessions" to the Journal du Dimanche, said that Merah seemed more obsessed with himself than with his cause. "He wanted to give himself a starring role," the source said. "He had a narcissistic need to seem important."
Mysteries and confusions remain. Did Merah act as a lone sympathiser of al Qaeda as he claimed, or under orders of an al Qaeda splinter group? He told the negotiators he had "personal training" in Waziristan on the Afghan-Pakistan border. But investigators are sceptical and hope some uncertainties will be solved by the questioning of Mohamed Merah's older brother, Abdelkader Merah, 29.
A magistrate from the judicial anti-terror unit yesterday extended the older Merah's custody. Abdelkader Merah faces formal accusations in the next few days of "complicity in assassination" and of "associating with wrong-doers who were planning acts of terrorism".
Investigators believe the brother was present when Mohamed Merah stole the Yamaha scooter he used in attacks.
Mobile phone records suggest that he was not far from the Ozar Hatorah school last Monday, when Mohamed Merah shot a teacher and his two sons, aged four and five, and a girl aged seven.
However, contrary to previous reports, no arms or explosives have been found at Abdelkader Merah's home.
Mohamed Merah's mother and sister-in-law, arrested last week, have been cleared of involvement in the murders and released. The fate of his mother, to whom he remained close, was one of the only regrets expressed by Mohamed Merah in his recorded conversations with police during the siege of his flat.
The gunman's state of mind is an important part of the investigation - but it could also become a political, and electoral, football. It suits Mr Squarcini and other security chiefs to "place" the assassin as a part-terrorist-part-psychopath - but it does not necessarily suit their ultimate boss, President Nicolas Sarkozy. With four weeks remaining to the first round of the presidential elections, Mr Sarkozy hopes the events in Toulouse will steer the campaign permanently onto two of his favoured issues: security and Islam.
The President spoke immediately after Mohamed Merah's death of the importance of "national unity" and urged French people not to "stigmatise" Islam.
But he and his campaign chiefs have been using the Toulouse attacks to brand the Socialist Party front-runner, FranAois Hollande, as being soft on crime and on terrorism. In a speech on Saturday, Mr Sarkozy repeated these accusations and then hardened previous campaign messages, borrowed from the far right National Front, which play with French fears of "Islamisation".
Previously, Mr Sarkozy had said that he would not allow Halal meat in state schools. This weekend, he said that he would insist that all children in state schools eat the "same menu" - implying, perhaps clumsily, that Muslim and Jewish children should be obliged to eat pork in school canteens. Mr Sarkozy has also proposed measures to respond to Islamist terrorism, such as making it a criminal offence to visit websites which promote hatred and violence.
The Socialist camp has been torn between trying to emphasise the "social" and "psychological" explanations of Merah's crimes and the fear of being painted as feeble on security issues. On Saturday, Mr Hollande attacked the failures of Mr Sarkozy's own security record in office.
Opinion polls suggest the Toulouse killings have slightly increased support for Mr Sarkozy but have not yet given him the big bounce that his campaign expected. Mr Sarkozy and Mr Hollande are running neck and neck in polls for the first round on 22 April.
Mr Hollande is still ahead in polls based on the two-candidate run-off on 6 May.
- Independent