The fugitive Strasbourg man suspected of shooting and knifing people at the French city's Christmas market has more than two dozen prior convictions and turned radical Islamist in jail, officials say.
Neighbours remember Cherif Chekatt as an ordinary local guy, but to security agencies the 29-year-old has represented a potential threat for some time, with his beliefs becoming hardened behind bars.
Chekatt grew up in Strasbourg's Cite du Hohberg, a large, tough housing estate built in the 1960s, where he lived at his parents' apartment.
He has 27 criminal convictions for theft and violence, officials said, and has spent time in French, German and Swiss prisons.
Authorities say he was flagged for radicalism in prison in 2015 and put on the "Fiche S" radical watch list then.
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.
"He had spent quite a bit of time in prison and since then we didn't see him much," said a 20-year-old youth who has known Chekatt since he was young, withholding his name.
"He had a radicalised big brother who was always in a djellaba, always at the mosque.
"It's frightening when you know he lived just next to you."
Police have taken into custody Chekatt's father, mother and two brothers and were interrogating them on Wednesday.
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.
The rampage surprised neighbours.
"It's a shock. We ask ourselves questions when something like this happens, especially as it is a calm area," a teenage acquaintance of Chekatt said.
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 labelled Fiche S does not forecast the level of threat they may pose," the deputy minister said.
Australian Associated Press