Investigators are trying to determine the cause of a head-on train crash in southern Italy in which 23 people were killed.
They are focusing in particular on the antiquated telephone alert system used to advise station masters of trains running on the single track.
Recovery operations using a giant crane and rescue dogs continued throughout the night and into today to remove the mangled debris after the two commuter trains slammed into one another in the Puglia region just before noon on Tuesday.
After visiting the crash site between the towns of Andria and Corato, Premier Matteo Renzi declared it an "absurd" tragedy and vowed to investigate fully. His transport minister was due to brief parliament later on Wednesday.
Union leaders and railway police blamed human error, noting that that particular stretch of track did not have an automatic alert system that would engage if two trains were close by on the same track.
Instead, news reports said the alert system relied on station masters phoning one another to advise of a departing train.
"Surely one of the two trains shouldn't have been there," said railway police Commander Giancarlo Conticchio. "And surely there was an error. We need to determine the cause of the error."
Italian Red Cross workers were shuttling family members to the morgue in Bari, the regional capital, on Wednesday to help identify the dead.
Coroner Franco Introna told the Ansa news agency that 22 bodies were at the morgue, with a 23rd expected to arrive later from Andria.
Passengers described being thrown violently forward at the moment of impact, and then trying to free themselves from the tangle of metal, body parts and debris in the scorching midday sun.
"I don't know what happened, it all happened so quickly, I don't know," one woman, who is eight months pregnant, told the Associated Press. "I saw my mother on the ground, my father and my sister bleeding, I don't know, I don't know, even I don't know."
One elderly couple described their ordeal to local television Telesveva. The man, his head covered in gauze, said he was knocked to the ground, while his wife, still barefoot, described how she came across body parts as she freed him.
"I pulled him from under the debris, myself barefoot, from under the debris and metal," the woman, who was not identified, told local TV. "I went to my husband screaming. I pulled him by the legs and feet. I climbed past people in pieces. How sad - there was nothing I could do."
Corato Mayor Massimo Mazzilli said debris was scattered over the countryside.
"It's a disaster as if an airplane fell," he said on his Facebook page, where he posted photos of the crash.
Pope Francis sent a telegram to the Archbishop of Bari, Monsignor Fracesco Cacucci, saying he shared in the pain of so many families. He said he was mourning those who died and praying for the injured to recover quickly.
The trains were operated by a private, Bari-based rail company, Ferrotramviaria, which connects the city of Bari with Puglia towns to the north and the airport. Ferrotramviaria's website said its fleet comprises 21 electric trains, most with four cars each. The line serves mostly students and commuters.
In a phone interview with state TV, Ferrotramviaria director-general Massimo Nitti said the dynamics of what went wrong are still to be determined, but it is clear "one of the trains wasn't supposed to be there".