Istanbul, Turkey ? Three crew members were arrested after a train derailed in northern Turkey, killing 37 people, but critics accused the government Saturday of using the detentions to deflect blame.

Union group and engineers said transportation officials approved the high-speed train project, despite accusations that the country’s aging rail system couldn’t handle the faster train. Prime Minister Recep Tayyip Erdogan personally inaugurated the project last month, brushing aside safety concerns raised by experts.

In an accident highlighting concerns about railroad safety in Turkey, four cars in a 25-car freight train also derailed Saturday in southern Turkey, officials said. No one was hurt.

Late Friday, the crew chief in charge of the passenger train, Koksal Coskun, and two engineers, Fikret Karabulut and Recep Sonmez, were formally arrested, a local police official said on condition of anonymity.

The official refused to elaborate, but private NTV television said the three were charged with negligence in the crash near the small village of Mekece, about halfway along the train’s route from Istanbul to Ankara. It was among the worst train crashes in Turkish history.

Officials had ruled out sabotage as a cause for the crash, but it was still not clear why the train derailed. Transport Minister Binali Yildirim said the train was traveling 23 mph over the speed limit of 50 mph during Thursday’s accident.

However, the attorney for the three men arrested, Ismail Gurses, showed reporters railroad-issued regulations for the trip that listed the speed limit in the crash area as 80 mph. The regulations were also published in Turkish newspapers.

“The reason for the crash could be aging infrastructure,” Gurses said. “The rails may have expanded or there may be a technical reason that we don’t know, but it’s definitely not because of high speed.”

Suleyman Karaman, the head of the railroads, told the Anatolia news agency Saturday that the accident might have occurred because the engineers slammed on the brakes when they noticed they were traveling around a bend too quickly. A study conducted by the railroad also showed that no other train had exceeded 50 mph during the previous week.

Turkish newspapers, however, blasted the government, accusing it of trying to orchestrate a cover-up.

“Somebody is fooling us,” headlined Radikal.

Mehmet Soganci, the head of a trade group for engineers and architects, accused officials of “putting political profit before human life.”