A second person was being held Friday over a shooting at a French school where a heavily armed teenager opened fire, slightly wounding three fellow pupils and a teacher, a judicial source said.
The suspect is a brother of a friend of the 16-year-old attacker, the source said, asking not to be identified by name. The friend is still being sought by police.
The shooter, who was described by investigators as unstable and obsessed with guns, surrendered to police after Thursday's attack in the southeastern town of Grasse.
Armed with a rifle, two handguns and grenades he caused panic at Alexis de Tocqueville high school, firing several shots.
A source close to the investigation said Friday that the weapons belonged to his parents and grandfather.
Described as a loner who had difficult relations with some fellow pupils, he had shown a fascination with violence and US school massacres, including the 1999 Columbine killings.
Prosecutors have opened an investigation into attempted murder.
The head teacher, who was shot in the shoulder after intervening to protect a group of pupils, was praised as a hero for having prevented a more serious attack.
The shooting at Alexis de Tocqueville high school rattled the quiet hillside town of Grasse, known mainly for its tradition of perfume production.
France is still in a state of emergency after a series of terror attacks, including the November 2015 massacre in Paris and a truck attack in Nice, just 40 kilometres (25 miles) from Grasse, in July last year.
Many feared the worst when news first filtered through of the violence, with elite police response teams immediately dispatched to the scene.
US-style school shootings are almost unheard of in France, which has low levels of gun crime.
In all, 14 people were injured, most of them hurt in a stampede triggered by the shooting.