Fifteen pensioners died in Tucumán province on Monday when the bus they were travelling on rolled off the side of the road.
The tragic accident happened in heavy fog in the province on a road with poor signage and blurred road safety demarcations on the bitumen.
Prosecutor for the district of Concepción Edgardo Sánchez said his main hypothesis was that the driver of the vehicle had performed an "unfortunate manoeuvre" that cost the lives of many of the passengers on board.
He requested the court detain the driver, Cristian Salinas, and his assistant, Gustavo Montoro, under a preventative arrest warrant to ensure "they remain in the province". A blood alcohol test was conducted on the driver, Sánchez told the TN news network. Both men stand accused of manslaughter and also suffered injuries in the crash.
Residents of nearby districts reported the poor visibility on the road at the time of the accident due to fog.
"This is an area of frequent accidents because of the signalling, the road demarcations and the lighting", one man, Jesús Ortiz, told La Gaceta de Tucumán newspaper.
Another man, Rolando Luna, who lives 100 metres from the crash site, gave greater detail: "I heard a big crash when I was drinking mates with wife. I thought a sugar cane cart had flipped over. I went out to see what had happened but the sun was coming up and because of the fog I couldn't even see my hands. I got to the crossing and found this terrible situation".
"People were screaming in despair. There was one man whose body was partly stuck under the bus and he was alive. I brought a shovel and started digging to try to get him out. There was blood and body parts everywhere", he said.
The bus involved in the crash belongs to the company Destino Cero. It had left Mendoza on Sunday night on route to the Río Hondos thermal springs in Santiago del Estero vía Tucumán.
The accident happened on Route 157 near La Madrid.