The wreckage of a carriage lies on a field near the railroad as recovery operations continued a day after two commuter trains slammed into one another just before noon Tuesday in Puglia, between the towns of Corato and Andria, Italy, Wednesday, July 13, 2016. Delayed rail improvements and the antiquated telephone alert system will be considered as part of the investigation into the violent head-on train crash in southern Italy that killed nearly two dozen people, officials said Wednesday. (Milena di Mauro/ANSA via AP)

MILAN - Italian prosecutors said Thursday their investigation into a fatal head-on collision of two commuter trains would look beyond human error, while media quoted a station master who acknowledged clearing one of the trains to depart.

The Turin daily La Stampa on Thursday quoted Vito Piccarreta, the station master at Andria, as saying "I let the train depart, I was the one who raised the signal." The 24-year railway veteran said there was confusion along the single-track rail line due to delays. Corriere della Sera quoted him as saying Tuesday's disaster "wasn't only my fault."

Twenty-three people were killed just before midday Tuesday when the trains, operated by the regional rail company Ferrotramviaria, collided violently on a single-track rail line where the right of way is controlled by phone contact, not by automated systems. More than 50 people were injured, with 21 still hospitalized, according to ANSA.

Questions about the crash include why the method of control hadn't been upgraded to newer technology, and why the station masters in Andria and Corato weren't aware that each had set a train on a collision course.

Prosecutor Francesco Giannella declined to confirm reports that the station masters had been formally placed under investigation, and indicated that the probe wouldn't focus solely on human error.

"To speak of human error is correct, but it is too much of an oversimplification," he told reporters.

He confirmed that magistrates were working alongside the financial police on a second line of investigation to determine why a second track hadn't been constructed despite EU and national funding.

The head of Italy's anti-corruption agency told the Senate that deep-rooted corruption in the nation's infrastructure projects probably played a role in the crash.

"It is probably the result of human error, but also probably the ugly consequence of an endemic problem in our country, the difficulty of creating adequate infrastructure, and one of the objective and certain reasons is included in the arguments we are making here today," Raffaele Cantone said in his annual address on corruption in Italy.

Asked to respond, Giannella said it wasn't yet clear what role corruption may have played in the collision, but he said in general terms that "it is clear that an excess of bureaucracy ... is a source of inefficiency, and corruption lurks in inefficiency, as everyone knows."

News from © The Associated Press, 2016