As his patrol monitored the promenade in the coastal resort of Cambrils, 120km from Barcelona, five terrorists drove into the resort intent on causing further death and destruction.
Driving at high speed, the jihadists ploughed an Audi A3 into pedestrians on a promenade before crashing into a police checkpoint - overturning the vehicle and injuring one officer.
The terrorists, who were wearing fake suicide vests, then jumped out armed with an axe and knives.
But using his army training and experience, the quick-thinking officer pulled his weapon and shot dead four of them, probably saving dozens of lives.
The fifth terrorist got away and stabbed a woman in the neck before being shot dead by another officer.
The black Audi A3 used in the Cambrils attack was photographed by a speed camera near Paris about a week before the atrocities in Spain, it emerged yesterday.
French police found the photo while searching for possible accomplices, according to security sources.