Colombian police arrested 15 presumed collaborators of the country's second largest rebel group in connection with simultaneous bombings that shook the capital last week.

The arrests took place Wednesday in coordinated raids on residences throughout Bogota. Among those taken into custody were two individuals who worked as contractors for the city government while others have ties to student groups.

President Juan Manuel Santos blamed the National Liberation Army for detonating the homemade explosives outside two offices of a pension fund owned by Colombia's richest businessman. Ten people were injured in the blasts, one which went off in a wealthy district unaccustomed of late to such violence.

The motive for the attacks is unclear but the ELN has been blamed for several small attacks in the capital the past year.