A speeding commuter train slammed into another that had stopped between stations during the morning commute Thursday in suburban Buenos Aires, killing three passengers and injuring more than 300 on a line that has been under government control since a deadly crash last year.

The state-run train agency dismissed possible brake failure as a cause and suggested that the conductor was at fault.

Satellite images show the train had braked normally at the previous station, and then rolled past four functioning warning signals without stopping before crash, the agency said. "Before a warning signal, the conductor should completely stop the formation, a situation that did not happen."

Instead, the train accelerated continually from the moment it left the previous station, reaching a speed of 38.5 mph (62 kph) on impact, Transportation Minister Florencio Randazzo said. That's three times faster than the speed on impact of the train that crunched into the downtown Once station on the same line in 2012, killing 51 passengers and injuring more than 700.

The conductors and their assistants on both of the trains involved in Thursday's crash were ordered detained by a judge for investigation on charges of "wreaking havoc followed by death," the state news agency Telam reported.

Randazzo asked for patience and vowed that those found responsible will be punished. He also said that the train workers passed alcohol breathalyzer tests before their shifts, a safety measure the government imposed after the previous crash.

"I feel rage, and impotence," President Cristina Fernandez said Thursday night, adding that she doesn't want to blame anyone in particular just yet. "I want the justice system to say what happened."

Argentina's independent auditor general, Leandro Despouy, who delivered a blistering report on the causes of last year's crash, suggested that the problems are systemic, due to many years of mismanagement, corruption and disrepair.

"We've been warning that this tragedy could happen again," Despouy told Radio de la Red. "Today it's a courageous move to travel by train."

The train slammed into the back of another at 7:07 a.m. between the stations of Moron and Castelar on the Sarmiento line, which links the Argentine capital's densely populated western suburbs to the downtown Once station.

Witnesses described the impact as "explosive," shaking the walls of nearby homes and derailing several of the train cars.

Some passengers were able to stumble out of the wreckage and walk along the tracks in the pre-dawn darkness, while many others waited for rescue workers to pull them out.

The provincial health ministry said at least three passengers were killed and 315 injured. Some suffered skull fractures and exposed broken bones, said Marcelo Marmonto, who directs the Luis Guemes hospital in Haedo.

At least five of the injured were in very serious condition, and one youth's leg had to be amputated, Gov. Daniel Scioli said after visiting with some of the victims.

Passengers on the Sarmiento line are accustomed to squeezing into extremely crowded cars during peak commuting times, but these trains had many fewer people on board because they were headed outbound from Argentina's capital.

Union leader Ruben Sobrero defended the workers and said the train should not have been brought into service. It had been in the shop for six months, then brought online, only to be withdrawn again because of brake problems, he said. Union members had warned of brake dangers, but it was brought into service anyway, Sobrero alleged.

Randazzo, named by Fernandez to improve the commuter rail system after last year's fatal crash, said a "black box" recording the train's movements would point to those responsible, but he too cast doubt on brake failure. "It had new brakes," he insisted.

Opposition politicians said the government bears blame.

"The accident puts into evidence the absence of the state, the laziness and the lack of concern for the life of the citizens," Radical party congresswoman Elsa Alvarez said in a statement. "Is this the transportation revolution the national government has been announcing?"

After last year's wreck at the Once station, which also injured 700 people, Fernandez promised to prosecute anyone responsible and make new investments in safety. She revoked the concession run by Mario and Sergio Cirigliano, two brothers who own many companies involved in maintaining Argentina's rail systems, and formed a state-supervised consortium of companies to operate the commuter lines.

The Cirigliano brothers, along with two former transportation secretaries, are among 28 defendants awaiting trial on criminal charges stemming from last year's crash, but they remain deeply involved in Argentina's train system.

It was the Cirigliano brothers' shop that worked on the brakes of the train that failed to stop in time Thursday.

"The train that hit the other was repaired in EMFER, which is controlled by the Ciriglianos, the businessmen responsible for the tragedy," said Paolo Menghini, who lost his son Lucas in the Once station crash, according to the local DyN news agency. "They cannot be sending trains to be repaired at EMFER."

But Randazzo said the government has no choice but to keep using the Ciriglianos' businesses, because the need for train repairs is so great that all available resources in the country are already at maximum capacity.