French police officers control a car at the French-German border following a shooting in Strasbourg, eastern France, Wednesday, Dec. 12, 2018. A man who had been flagged as a possible extremist sprayed gunfire near the city of Strasbourg's famous Christmas market Tuesday, killing three people, wounding 12 and sparking a massive manhunt. France immediately raised its terror alert level. (AP Photo/Christophe Ena)

STRASBOURG - The fugitive Strasbourg man suspected of shooting and knifing people as he shouted "Allahu Akbar" at the French city's Christmas market is a criminal who turned radical Islamist in jail, officials say.

Neighbours remember Cherif Chekatt as an ordinary local guy, but to security agencies the 29-year-old had represented a potential threat for some time, his beliefs hardened behind bars.

Chekatt grew up in the Cite du Hohberg, a large, tough housing estate built in the 1960s, where he lived at his parents' apartment in the Rue Tite Live.

He has 27 criminal convictions for theft and violence, officials say, and has spent time in French, German and Swiss prisons. Now police are seeking him as the suspect who killed at least two people on Tuesday night.

Neighbours said they believed Chekatt's brother was a radicalised Muslim but had always seen Cherif as a typical young man who dressed in jogging pants and trainers, unlike his sibling who preferred a traditional robe.

This undated handout photo provided by the French police, shows Cherif Chekatt, the suspect in the shooting in Strasbourg, France on Tuesday Dec. 11, 2018. Picture: French Police via AP.

"He had spent quite a bit of time in prison and since then we didn't see him much. He had a radicalised big brother who was always in a djellaba, always at the mosque," said a 20-year-old youth who has known Chekatt since he was young, withholding his name. "It's frightening when you know he lived just next to you."

Police were interrogating Chekatt's father, mother and two brothers on Wednesday in custody.

France has long struggled to integrate western Europe's largest Muslim population, for years mired in a virulent debate over national identity and the role of Islam in a country that holds fast to state secularism.

A wave of militant attacks since 2015, most of them commissioned or inspired by Islamic State, has killed about 240 people and exposed France's difficulties in tackling homegrown militants and jihadists returning from wars abroad.

Strasbourg deputy mayor Robert Herrmann said about 400 people living in and around Strasbourg were on the security agencies' "Fiche S" watchlist, including the suspect.

"We know this risk and we trust our services to put an end to these murders," he said, before adding: "There will, though, always be a way through the net."

WATCHLIST

Deputy Interior Minister Laurent Nunez said Chekatt had been radicalised in jail, becoming an apologist for terrorism, but there had been no signs he would turn violent.

"He encouraged a radical religious practice in prison but nothing indicated that he would carry out an attack," Nunez said on France Inter radio.

Police said the attack followed a police search of Chekatt's flat in Strasbourg in a homicide investigation on Tuesday morning. Chekatt was absent, but a .22 calibre Long Rifle and four knives were found.

A German security source said that following a conviction for "aggravated theft" Chekatt had been jailed in the southern German city of Constance from August 2016 to February 2017.

He was released before the end of his two-year, three-month prison sentence into the custody of German police so that he could be deported to France.

A second German security source said he had been banned from re-entering the country.

Several German officials and sources said Chekatt had not been identified as a security threat. It was not immediately clear if or how French officials had communicated their concerns to German authorities.

The rampage surprised neighbours. "It's a shock. We ask ourselves questions when something like this happens, especially as it is a calm area," said a teenage acquaintance of Chekatt.

Nunez said more than 20,000 people in France were designated as Fiche S and that a little over half of those were being monitored.

"We follow many individuals like him ... Being labeled Fiche S does not forecast the level of threat they may pose," the deputy minister said.

Reuters