Superintendent Mario Yanga, city police chief, ruled out terrorism in the 12:45 a.m. blast that killed Ryan Wee and George Manicap at the billiard hall along Paseo de Putik Drive in Barangay Putik.
Police said the grenade thrower, former Marine Benjamin Rivera, was among those wounded, who included his wife, Nenita and son Benhar, Jacinto Comato, Richard Bucog, Tommy Española, and John Raymond Galvez.
Investigators said Rivera, who has had a history of malaria, allegedly got irked when a beer bottle fell and broke on the floor of the billiard hall.
Rivera then left the hall packed with a dozen of teenagers but later returned with a grenade.
"We just heard a clicking of the lever as the suspect pulled the pin of the grenade and it exploded while still on his hand (severing his right arm)," a witness said.