MPs from across the political spectrum this week condemned Transport Minister Oscar Puente for attributing Wednesday's crash to a break in protocol by control centre operators rather than accepting responsibility, with rail workers' unions calling for his immediate dismissal.
The crash, which happened near the town of Urda in central Spain, followed another accident involving the same rail companies on the same line that left 46 dead in January.
It has reopened a debate about safety and maintenance on Spain's high-speed rail network, the most extensive in Europe, as the country prepares for an election that progressive Prime Minister Pedro Sanchez has called for November 29.
"My duty now is not to focus on discussing whether I will remain in office but on solving the problem, determining exactly what happened and providing clear explanations," Puente said at a press conference on Friday.
The train that smashed into a second stationary one was travelling at a speed between 160 and 200 km/h when the crash occurred, according to a preliminary report released on Thursday by the Independent Authority for the Technical Investigation of Accidents and Incidents (AITAT).
"The sequence of malfunctions, instructions and actions eventually led to the collision, in the absence of the necessary mitigating barriers," AITAT said in the report.
AITAT said it would not be able to confirm the exact speed of the train until it extracted information from the train's black box.
At the scene of the crash, large cranes were lifting the mangled wreckage as the Civil Guard listed 64 people as missing in what is already Spain's deadliest train accident since 2013.
Authorities have carried out 49 autopsies so far and formally identified five people - three women and two men - Esther Padilla, spokeswoman for the Castilla-La Mancha regional government, said on the TVE network.
"Testing is proceeding slowly, although families will be contacted throughout the day so that they can come and collect their results," Padilla said on Friday.
It was unclear if all those missing were accounted for in the death toll.
No additional bodies were found when rescue teams overturned a train carriage on Thursday, Castilla-La Mancha regional leader Emiliano Garcia-Page said on TVE.
Identifying the bodies was proving difficult because many were in pieces, he said.
On Thursday, rescue teams had placed partial remains in 31 bags.
"The truth is that we cannot rule out the possibility that there may be more fatalities," Garcia-Page said.
As identification of the dead continued, the debate about who was at fault intensified, with unions saying it was unfair to lay the blame on human error.
Sanchez on Friday vowed to find out what caused the accident.
"It is unacceptable for a country like Spain, with such a strong high-speed rail system, to suffer two accidents of this nature and magnitude in a single year," the prime minister said.
The collision occurred after several trains were automatically stopped due to the failure of a signalling system, after which the central control centre in Madrid took over.
A train operated by state-owned Renfe was authorised to proceed, even though there was a stationary Iryo-operated train ahead, according to Puente.
