The investigation into Tuesday’s head-on train crash in southern Italy that killed 23 people is focusing on the antiquated alert system on the line.
They are looking into one of the black boxes recovered at the scene of the collision, on a remote single-track line north of the city of Bari.
The system relied on telephone calls and “human error” remains the main line of inquiry, reports say.
Dozens of rescue workers are still searching the wreckage.
The inquiry is focusing on the lack of automatic signalling system on a small part of the Italian railway network.
The stretch of track between the towns of Andria and Corato in the southern region of Apulia where the crash happened did not have an automatic alert or brake system.
It relies on station masters phoning one another to advise of trains running on the single track.
“Surely one of the two trains shouldn’t have been there,” railway police Cdr Giancarlo Conticchio is quoted as saying by the Associated Press news agency.
“And surely there was an error. We need to determine the cause of the error,” Mr Conticchio said.