It is now thought that the explosion at a relay station in Hernani was part of a plan to lure police officers into the area, at which time a second device would detonate.
The explosion at the Mount Santa Barbara relay station, an isolated area, occurred at around 01:00 on Friday morning, but the police delayed an inspection of the area until dawn.
Police officers then discovered a backpack at the site with a cable, just visible, running across the road. Explosives experts are examining the backpack and its contents.
Had the police officers rushed in to investigate, the consequences could have been tragic. As it was, no-one was hurt in the explosion.