FONTAINES-SUR-SAONE, FRANCE—The top suspect in the beheading of a businessman that French authorities are calling a terrorist attack took a “selfie” photo with the slain victim and sent the image via WhatsApp to a Canadian mobile phone number, officials said Saturday.

French investigators were working to determine the recipient’s identity, but weren’t able to immediately confirm media reports that it was an unspecified person now in Syria, where the radical Islamic State group has seized territory, the security officials said.

The revelation added a macabre twist to an investigation that has not turned up a solid link to radical or foreign groups, but has revived concerns about terrorism in France less than six months after deadly attacks in the Paris area.

Top suspect Yassine Salhi, a truck driver with a history of radical Islamic ties, as well as his sister and wife remained in police custody in the city of Lyon, a day after he allegedly crashed a truck into a U.S.-owned chemical warehouse and hung his employer’s severed head on a factory gate, officials said.

One of the officials said the selfie was forwarded via WhatsApp, the globally popular instant messaging system owned by Facebook, to a phone number in Canada. The officials spoke on condition of anonymity because the investigation was ongoing.

Royal Canadian Mounted Police spokeswoman Josephine Laframboise had no immediate comment on the report.

Jean-Christophe de Le Rue, a spokesman for Canada’s Public Safety Minister, confirmed that Canadian authorities are involved in the case.

“While I cannot comment on operational matters of national security, we are assisting the French authorities with their investigation,” he said.

He declined to comment further on details of the investigation.

No group immediately claimed responsibility. The severed head appeared to mimic Islamic State’s practice of beheading prisoners and displaying their heads for all to see, and came days after the militants urged attacks during the Muslim holy month of Ramadan. French authorities say Salhi had links to radical Salafists in the past.

Paris prosecutor’s office spokeswoman Agnes Thibault-Lecuivre said the leading suspect began speaking with investigators after first refusing to do so. She declined to provide details, but said investigators haven’t found any foreign connection.

The site of the beheading wasn’t yet known to investigators, and the victim had been strangled beforehand, she said.

A fourth person arrested Friday was released without being charged. Under French anti-terrorism laws, Salhi and the women can be held up to four days before either being released or handed preliminary charges and locked up.

President François Hollande’s office said he will convene a meeting with top parliamentary leaders about the matter on Tuesday.

Separately on Saturday, hundreds of people turned out in the region to honour slain businessman Herve Cornara and denounce the violence. Dozens turned out for a minute of silence in Saint-Quentin-Fallavier, the town southeast of Lyon where Friday’s attack took place at an Air Products chemicals warehouse.

Several hundred people also gathered outside a housing project in the town of Fontaines-sur-Saone to honour Cornara, 54, the manager of a transportation company that had employed Salhi since March. They recalled a kind, humble man who was active in the community of the Lyon suburb.

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“He lived on the fifth floor, me on the fourth. He spoke with all the young people in the neighbourhood. He didn’t differentiate between (non-Muslim) French and Muslims,” said Leila Bouri, a 24-year-old cafeteria cashier. “If you ever had a problem, you would go see him.”

“When I heard this, I was shocked. It’s shameful,” she said. “I am a Muslim, but you can’t kill like this. It’s not who we are. In Islam, we’re not told to slit throats. We only slit the throats of sheep. You don’t slit the throats of people.”

The suspected killer, she added, “isn’t a Muslim in my opinion.”