The municipal government in the northwestern Colombian city of Medellin announced Monday that five apartment buildings will be demolished that were left standing in the Space residential complex after the sixth collapsed, leaving 12 people dead.

The decision was based on a study by the University of the Andes which concluded that the construction of the six 24-story buildings did not comply with the seismic-endurance regulation and that "structural deficiencies" exist in all of them.

According to experts' recommendations, the demolition will be carried out in four steps, Medellin Mayor Anibal Gaviria said.

The technical study concluded that, because of its design, the Space towers act as a single structure and a risk of collapse exists for the five still standing.

Investigators did not establish in their report who was responsible for the collapse of Tower 6, which came crashing down the night of Oct. 12, one day after its residents were evacuated because of the enormous cracks that appeared in the structure, thus avoiding a far greater tragedy.

Eleven people - workers and engineers working to repair the structure, a watchman and a resident who had returned home - died when the tower fell, while another watchman was seriously injured and died some time later. EFE