Yassin Salhi was a quiet man with a job, a family and no criminal record before he allegedly launched a grisly assault at an industrial gas factory in France and pinned his boss's severed head to the fence on Friday, reports Yahoo! News.
While authorities had investigated the married 35-year-old father of three for ties to the radical Salafist movement, he was never identified as participating in terrorist activities and never convicted of a crime.
A co-worker of Salhi's said he was mysterious, possessed of a quiet strength and deceptively calm.
"He was a wolf in sheep's clothing," Abdel Karim told RTL radio.
"He had already talked to me about Daesh," said Karim using one of the names for the Islamic State group.
It was "not to indoctrinate me into anything, but simply to ask me my opinion. When I told him what I thought, from that day on, it was 'Hello/goodbye.'"
Salhi caught the attention of intelligence authorities in 2005 and 2006 because he was socialising with a group of people associated with radical Islam, a source close to the case told AFP.
Intelligence services investigated him for a few years thereafter, but did not renew their inquiry in 2008, French interior minister Bernard Cazeneuve said.
"This individual has links with the Salafist movement, but had not been identified as having participated in activities of a terrorist nature," he added.