The mother of a man who is believed to have stabbed a German tourist to death near the Eiffel Tower in Paris had expressed worries about her son a few weeks before the incident, according to a prosecutor.
Two more people, including a man from Britain, got hurt in the attack on Saturday.
A 26-year-old man from France was arrested, and officials who investigate terrorism are looking into the case.
The French minister inside the country said the person who attacked failed to receive proper care for their mental health.
Gérald Darmanin said to BFM TV that the person who attacked had a serious mental illness. He also said that doctors had mentioned on a few occasions that the person was getting better, acting more normal, and could be released from care.
Prosecutor Jean-François Ricard said the suspect promised to support the Islamic State group (IS).
The prosecutor said that Armand R, who was born in France to Iranian parents, became a Muslim when he was 18 years old. In 2016, he was sent to jail for four years because he wanted to go to Syria and join IS.
Mr Ricard said the police were watching the suspect because they thought he might be involved in extremism. They have also arrested three people, including some of his family, for questioning.
He said that the attacker’s mother told the news that she was worried about her son’s behavior because he had become withdrawn and quiet in late October.
But, there wasn’t enough information to start a new trial, he said.
The police said the person they think did the bad thing was supposed to be getting help for mental health problems.
The person who died in the attack was a tourist from Germany who worked as a nurse.
Mr Darmanin said the person who got hurt was with his wife when someone attacked and killed him with a knife on Quai de Grenelle.
He said a taxi driver saved the wife’s life and the suspect ran away over a bridge over the River Seine.
After going to the other side of the river, he hurt two more people: a 60-year-old man from France and a 66-year-old tourist from Britain who got hit in the eye with a hammer.
The police used a Taser to stop the suspect and arrested them for planning to kill someone. They are also suspected of trying to kill someone as part of a terrorist plot.
The two hurt people got help from emergency workers and on Sunday, the Health Minister said to the French media that they were doing well.
A video posted online seemed to show the police catching the suspect with guns not too far from where the attack happened.
Mr Darmanin said the person who attacked was heard shouting “Allahu Akbar” and told police that he was upset because many Muslims are dying in Afghanistan and Palestine.
The suspect also said that France helped cause the deaths of Palestinians in Gaza.