A local police official says investigators were interviewing two friends of the 16-year-old student who shot at three students and the principal at a high school in the southern French town of Grasse.
One young man was arrested overnight and his twin brother was arrested Friday. Both were said to be close to the suspect, the official said.
The official spoke anonymously because he was not allowed to provide information on an ongoing investigation.
Grasse prosecutor Fabienne Atzori said Thursday the motivation of the suspect stemmed from bad relations with his peers and there was no reason to suspect the shootings were terrorism-related.
Students on Friday went back to school, where psychological support was being offered.