French investigators call them the “gangster-jihadists” – young men, often from poor immigrant backgrounds, who start with petty crime, drug dealing and robbery and graduate to terrorism.

They exist under the radar of the intelligence services or are placed on watch lists for their radical religious beliefs and subjected to varying degrees of surveillance – but are not expected to become violent.

In any case, French security forces have said it would be impossible to keep an eye on all 12,000 listed for suspected Islamist views or even the 4,000 considered “problematic”.

The profile of Chérif Chekatt, who is being hunted by police in connection for the attacks in Strasbourg, is all too familiar in France.

Chekatt was born in Strasbourg in February 1989, into a family with Moroccan roots, and appears to have fallen first into petty crime then gangster circles. The final stage, his apparent move into Islamic extremism, was reportedly sparked – or at least strengthened – during a spell in prison between 2013 and 2015.

Like many youths growing up on outer-city housing projects in France, home to many of the country’s north African immigrant population, where poverty and unemployment are rife, Chekatt left school early and had a series of low-paid jobs.

By the age of 29 he had 27 convictions for theft and violence, the public prosecutor Rémy Heitz said. On the morning of the Strasbourg attack, he was to have been arrested in connection with attempted murder linked to an armed robbery that went wrong last summer.

His religious practice and proselytising in jail were described by Heitz as “showing signs of radicalisation”. For that he was put on the fiche S list.

Since the watch list was established in 1969, 400,000 people have been added to it after being deemed a potentially serious threat to national security. Inclusion on the list makes the person subject to surveillance, but does not deem them guilty of any crime. Not all are terror suspects; gangsters and political extremists, anarchists and even radical environmentalists are also included.

Of the 20,000 currently on the fiche S only a dozen are thought to be under 24-hour surveillance.

The deputy interior minister, Laurent Nuñez, said Chekatt had been being watched in a “relatively serious manner”.

In 2016 Chekatt was added to the Fichier des signalements pour la prévention et la radicalisation à caractère terroriste (file of reports of the prevention and radicalisation of a terrorist nature), a little-known list, separate from the fiche S, of 20,000 people known to have been, or at risk of being, radicalised.

Five of his alleged accomplices were picked up in raids on Tuesday morning, but when police turned up at his apartment in a block at the Les Poteries district of west Strasbourg, Chekatt was not there. Inside, they found a stun grenade, a long rifle with ammunition and four knives, including two hunting knives.

French officials have suggested the prospect of another prison sentence could have sparked the Christmas market attack a few hours later.

“In prison he encouraged the practice of religion in a radical form, but there was nothing in his way of life to suggest he was planning to act,” Nuñez said.

Chekatt’s background has similarities with a number of other terror attacks in France.

Mohamed Merah, who gunned down three French soldiers and four Jewish civilians, including a rabbi and three children in a series of attacks in and around Toulouse in March 2012. Merah had been arrested numerous times for petty crimes and had 18 convictions by the age of 23.

The brothers Saïd and Chérif Kouachi, responsible for the attacks on the satirical newspaper Charlie Hebdo in 2015 when 12 people were killed, and Amédy Coulibaly, who, in a parallel operation, shot a policewoman and held hostages at a kosher supermarket in east Paris, killing four, all came from the capital city’s suburban housing projects and had fallen into petty crime.

Zied Ben Belgacem, shot dead at Orly airport in March 2017 after trying to grab a soldier’s gun to shoot others, had a lengthy criminal record of violence, robbery and drug-related offences.

Karim Cheurfi, who shot dead a police officer on the Champs Élysées in April 2017, had served more than 12 years in prison for shooting at police officers and had been jailed four times for attempted murder, violence and robbery.

Radouane Lakdim, who in March 2018 killed the gendarme Arnaud Beltrame who had taken the place of a female hostage, was also a convicted petty criminal.

The former anti-terrorism judge Jean-Louis Bruguière said Chekatt had the “typical profile” of a young radicalised Islamist.

“They are able to dissimulate their beliefs to the point where they drink alcohol or even ask their mothers to bring them a pork sandwich,” Bruguière told BFM TV. “In this way they are capable of passing under the radar but turning to violence extremely quickly.”

Residents in the housing block at Les Poteries where Chekatt lived were stunned – as were neighbours of all of the previous terror suspects.

“He was quiet. He didn’t speak much and was a bit of a loner; he didn’t hang around unless he was with his brothers and father,” said one of Chekatt’s neighbours. “He seemed normal. Just a normal guy.”