Paya's family -- and Carromero himself before being taken into custody -- holds that the car was rammed by another vehicle, presumably of secret police officials that had been following them for hours.
According to Spain's El Mundo newspaper, it has now been revealed that, during the time of his imprisonment, Carromero was administered an intravenous substance that kept him sedated for nearly two weeks and has since led to some memory loss.
Can't imagine why.
For those wondering, there are various drugs, e.g. Midazolam, which can be induced to cause a partial or complete loss of memory.