Senior Superintendent Conrado Laza, city police chief, said Chemuel Balanay, 19, and his 16-year-old brother were suspected to be involved in thefts in the Toril district where their mother resides, and in mall holdups.
Laza said the two were also in the watchlist of the Philippine Drug Enforcement Agency.
Laza believes that the Balanays were high on drugs when they went on a killing rampage in the Lacorte residence at Lanzona Subdivision, attacking with crowbars their own relatives, spouses Diosdado, 58, and Evelyn Lacorte, 48, the couples son-in-law Julius Villarmea, 22, and grandson Kenneth Villarmea, 9.
Wounded in the attack were Lacortes daughter Grace and her Japanese husband, Tomutso Hashigutzi, and three-year-old Maria Carla Beatriz Villarmea.