Security services had been tracking suspect Mohamed Merah since 2008

Mohamed Merah, the man suspected of the Toulouse killings, had been on a French security service "watch list" since 2008. He and his older brother, Abdelkader, have been on a list of possible suspects since the first in a series of three attacks and seven killings in eight days.

The younger Merah was arrested by US authorities in Afghanistan in 2008 and sent home to France, He travelled back to the Afghan-Pakistani border last year. He belonged to a small, extremist Islamist group, run by his brother, and regarded by security services as harmless. In the past four years, he twice applied to join the French army but was refused because of minor offences.

Although French authorities were congratulating themselves yesterday on locating Merah before he killed again, they also face awkward questions on why they failed to identify him as a serious threat earlier.

Merah, 23, was born in Toulouse in October 1988 of Algerian parents and was variously described by neighbours and acquaintances as a "quiet young man" and "the kind of person who would give you a hand if you needed it." Karim, 30, a neighbour who has known Merah since he was 13, told The Independent yesterday: "It was his brother who was always the extremist. Until a couple of years ago, Mohamed was just an ordinary guy. He worked in a car body repair shop. He played football. Then a couple of years ago, he lost his job and he seemed to go off the rails."

In fact, the internal security services believe that Merah first volunteered as a jihadist in 2007 or 2008. He attended training camps on the Pakistani-Afghan border. After returning to France, he appears to have joined a small group of extreme Islamists, run by his brother.

French authorities admitted yesterday that this group was under surveillance but not regarded as any particular threat. Abdelkader Merah was also under arrest yesterday, suspected of helping, or even masterminding, the attacks.

When a soldier was murdered more than a week ago, the two brothers were briefly suspects. Little was done to trace them until after the school slaughter.

An email, replying to a small ad, sent to one of the murdered soldiers was traced to Abdelkader Merah's computer. Someone answering Mohamed's description was also found to have visited a Yamaha motorbike showroom in Toulouse last week. He wanted to know how to de-activate the anti-theft, satellite location device on the kind of scooter used in all three attacks.