The train's "black box" recordings of conversations between the motorman and control room were already in the judge's hands, and other evidence abounds, from GPS data to cameras and other recordings as well as physical evidence from the wrecked train, he said.
With 703 injuries among the estimated 1,500 passengers, thousands of people desperately rushed around Buenos Aires checking lists of survivors and hoping their loved ones weren't in the morgue.
Many of the dozen or more hospitals that treated the injured said they had no unidentified patients, and by Thursday afternoon the morgue had identified all 50 fatalities.
The Bolivian Embassy announced that a pregnant consular official, Nayda Tatiana Lezano Alandia, was among the dead. She left behind three daughters, Argentina's state-run Telam news agency reported.
Sabrina Espindola, 29, who worked downtown by day and studied to be a surgical assistant until midnight each night, was pulled from the first car, her husband, X-ray technician Ezequiel Mercado, told The Associated Press. "She was getting her degree this year," he said, sobbing at the thought of retrieving her body at the morgue.
The body of Sofia Peralta, 19, also turned up at the morgue, while her brother Fernando, 18, was hospitalized with multiple leg fractures and damage to his arm and face.
"When he woke up, he remembered first his sister. We told him Sofia was gone. He looked at us for a while, then he went very quiet," their uncle Daniel Peralta said.
The siblings worked together as telemarketers at Nextel and took the train together every day, he said. "They were always together," Peralta said.
With the crash still unexplained, Thursday's commute was unnerving for some of the millions of people who have to ride the city's trains each day.
A woman who gave only her first name, Marta, said she abandoned one train after the motorman complained to passengers that he couldn't get the engine to work, followed by a lengthy delay and then lurching stops.
"I got down with the kid and said to myself: 'No, that's enough. I'm getting out of here,'" she said.
Associated Press writers Debora Rey, Paul Byrne and Roger Dwarika contributed to this report.
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