MANILA - The Department of Justice (DOJ) on Wednesday ordered the National Bureau of Investigation (NBI) to investigate the death of 14-year-old Reynaldo de Guzman, the companion of slain teen Carl Angelo Arnaiz.

De Guzman and Arnaiz, 19, both went missing on Aug. 17, when they left their homes in Cainta, Rizal to buy midnight snacks.

Arnaiz, a former University of the Philippines student, was found dead with multiple gunshots 10 days after he went missing. De Guzman's body was meanwhile found Wednesday in Nueva Ecija with several stab wounds.

"The National Bureau of Investigation, through Director Dante A. Gierran, is hereby directed and granted authority to conduct investigation and case build-up over the death of Reynaldo de Guzman, and if evidence so warrants, to file appropriate charges thereon," the department order read.

De Guzman was positively identified by his father at a funeral parlor in Gapan City, Nueva Ecija.

The father was able to confirm that it was his son through a mark on the boy's neck and a wart on the left knee.

• READ: Tadtad ng saksak: 14-yr-old companion of slain teen also found dead

Justice Secretary Vitaliano Aguirre II earlier ordered the NBI to conduct a parallel investigation into the death of Arnaiz, who was killed in a shootout with police after allegedly robbing a taxi driver.

Autopsy findings, however, suggested that Arnaiz was probably tortured, contrary to police's claim that he was killed in a shootout with lawmen.

De Guzman's death came amid public outrage over the killing of Arnaiz and 17-year-old Kian Loyd Delos Santos, both slain in questionable police operations in Caloocan City last month.

• READ: Duterte to pursue raps vs cops in Carl Angelo's killing

Authorities have yet to determine who was behind De Guzman's killing. -- Report from Johnson Manabat, ABS-CBN News