Officials in northern France are investigating if the derailment of a passenger train on Friday evening was the result of "a malicious act".
Prosecutor Sébastien Gallois said on Saturday that a fragment of rail had been found on the tracks - and the reasons for its presence were "unknown".
Local media say 186 passengers were on board the train that was operating between Rouen and Caen in Normandy.
Fourty-four were treated for injuries, including an 18-year-old woman who was airlifted to hospital in a critical condition.
Some 140 firefighters and other emergency teams were deployed to the scene of the incident near Cléon, just south of Rouen, shortly before 20:00 (18:00 GMT).
"Suddenly there were a few jolts, and then after about three seconds it got stronger and stronger," Louis, a passenger on the train, told ICI Normandie radio.
"I couldn't stay in my seat anymore. The windows partially shattered, the stones from the track came into the carriage. It was really shocking. I'm still shaking," he added.
The Rouen prosecutor's office said the train driver had tested negative for drugs and alcohol.
