A 20-year-old woman and a man, aged 28, died after the car they were in ploughed into a petrol station in Valencia and burst into flames.
A dog that was travelling with them in the car also died in the crash at the BP service station at kilometre 988 on the N-340, in the municipality of Benicassim, in Castellón.
No other vehicles were involved in the accident.
Witnesses have told police that prior to the fatal crash, at around 6am in the morning, they saw a girl being forced into a car.
Police are investigating reports that the girl ended their relationship in November.
It is further claimed that her mother went to the police in early December after the man had tried to run over her daughter.