Investigators said the killing was triggered by an old grudge between the families of the suspect, S/Sgt. Sala Ismael, who belongs to the Armys Quick Response Team, and the victim, PO1 Assis Sari.
Sari reportedly went to the Southcom headquarters to claim his rebate from the Armed Forces of the Philippines and Police Savings and Loan Association Inc. when Ismael spotted him.
Ismael, who was guarding Gate 2 of the Southcom, fired at Sari with an M-16 Armalite rifle, killing him on the spot.
"The incident was an isolated case and there is no cause for alarm as the fateful incident was triggered by an old grudge that stemmed way back from Sulu between the two families," said Maj. Bob Bacarro, Southcoms deputy information officer.
Investigation showed that Ismael had vowed to avenge the death of his mother who was reportedly killed by a relative of Saris in Sulu.
The Southcom is leaving it up to the police to file formal charges against Ismael, who surrendered to his superiors immediately after the incident.