French police have arrested two people in the eastern city of Strasbourg in connection with Saturday's fatal stabbing in the centre of Paris.
Officers are now questioning the parents and friends of the 21-year-old who had been flagged previously as a potential security risk.
The attack happened in the bustling Opera district, known for its many restaurants, cafes and the Palais Garnier opera.
The attacker shouted "Allahu akbar" (God is greatest) as he began his stabbing rampage.
He fatally stabbed a 29-year-old man and wounded four others before he was shot dead by police.
Who was he?
Judicial sources have identified the attacker as Khamzat A, without giving his full name. French media are reporting it as Azimov.
Government spokesman Benjamin Griveaux said since 2016 he had been on a counter-terrorism watchlist of suspected radicals who may pose a threat to national security.
Has anyone claimed the attack?
Yes. ISIL said they were behind it but have provided no proof. Griveaux said the claim had not yet been fully authenticated.
In a video which the SITE intelligence monitoring group said was posted by ISIL’s Amaq news agency, a young man described as the attacker pledged allegiance to Islamic State leader Abu Bakr al-Baghdadi.
Speaking in French, his face largely obscured by a black hood and scarf, he said “infidels” fighting ISIL were to blame. “You started it by killing Muslims,” he said.
It was not immediately possible to confirm the identity of the man in the video.
It was the latest in a succession of attacks in France since January 2015 in which more than 240 people have been killed.
What is the Strasbourg link?
Judicial sources said the assailant’s parents as well as a friend of his were being held for questioning.
The friend, arrested in the eastern French city of Strasbourg, was born in 1997, a source said.
French media report the attacker had lived in Strasbourg for a long time before moving to Paris last year.
And what about the Chechen link?
The attacker became French when his mother obtained citizenship in 2010, according to Griveaux.