No one was killed or hurt in the blast, which caused minimal damage to property since the explosive is not as powerful as modern grenades.
"It was an old fragmentation grenade," Senior Superintendent Marietto Valerio told The Star.
He was quick to assure that the explosion had nothing to do with recent bombings in Metro Manila allegedly carried out by the group Taong Bayan at Kawal, or Tabak.
Valerio said the grenade blast happened at around 6:15 a.m. in front of the Aqua Venture diving equipment shop located at the ground floor of a three-storey building at Saint Paul Road, Mayapis street, Barangay San Antonio.
Two still unidentified men on board a tricycle were seen passing by and hurling the vintage grenade before making a quick getaway.
Valerio said investigators were able to speak with the building owner, identified as Mario Sarmiento, who suspects that those behind the grenade attack include other tenants or workers who were not getting along well with his mother.
"We arrested nobody and are still investigating the incident. We were able to recover pieces of evidence like the body of the old grenade and the safety pin," he explained.
According to him, the vintage grenade could have still caused injury.
"Parang sumabog lang na gulong ng truck ang lakas. It seems that someone was trying to scare the owners," Valerio said.
Explosions in the metropolis are being treated seriously since the group Tabak supposedly launched attacks in Makati City, Quezon City, Manila, and Taguig.
The targets included the Grepalife Building, Police Community Precinct, bus utilized as a satellite police station and a van inside the National Capital Region Police Office (NCRPO) compound in Camp Bagong Diwa.
"These are threats on the country’s financial district. The security of private and public buildings in Makati and the people who live and work in Makati is a priority of the city government and a concern of the entire community. The response should involve the entire community," he said.
Binay has called to the conference all barangay captains, precinct commanders, and officers of the Makati Police, Makati Department of Public Safety, Fire Department, and the security officers of buildings, establishments and embassies located within the locality.
Binay said he is concerned that these attacks are intended to create an impression of a breakdown in peace and order.
"These bombings, and the threats of attacks, apparently are meant to create conditions that are beneficial to some powerful interests," he said. "It seems that the intention is to terrorize the population into accepting drastic measures against some groups who will be blamed for these incidents."