French authorities are investigating whether sabotage caused a regional passenger train to derail Friday evening in Normandy, injuring 44 people including one critically.

The train, carrying 186 passengers between Rouen and Caen, derailed near Cléon shortly before 8 p.m. local time on September 11. A piece of rail was found on the track and is believed to have caused the incident, according to police sources and the Rouen prosecutor's office.

Prosecutor Sébastien Gallois stated that the leading theory involves the rail segment on the tracks, with its presence under investigation. Drug and alcohol tests on the train driver returned negative. The train's black box has been seized, interviews are scheduled, and a court-appointed expert has been called in.

An 18-year-old woman was airlifted to hospital in critical condition but her life is no longer in danger, officials said. The remaining injured passengers received treatment and most have been discharged or are set to be.

Emergency responders deployed about 140 firefighters and other teams to the scene. Traffic on the line remains suspended.

Investigators are working to determine if the event was accidental or deliberate, with sabotage treated as the primary line of inquiry by police.

The incident comes amidst ongoing concerns over rail security in France and broader challenges with public safety and infrastructure protection.