Witnesses said Anthony Zepeda had argued with family members in their home in the town of Pili yesterday, police said.
The confrontation later culminated in Zepeda taking hostage his father, brother, sister-in-law and the maid, provincial police chief Superintendent Romero Bausa said.
Bausa said police negotiators had tried to end the crisis peacefully, but Zepeda instead shot his captives and later committed suicide.
"The cadaver of the suspect was also found at the ground floor. He has a bullet wound in the head and there's an indication that he shot himself," Bausa said.
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Bausa said Zepeda was also a known gun enthusiast as was his father.
"The assumption was... That he was fully armed," he said, explaining why police did not immediately assault the suspect's home.
The killings underscored the need for stricter gun controls in the Philippines, where a thriving weapons black market makes it easy for anyone to buy unlicensed firearms.
In January last year, a drugs-crazed gunman armed with a semi-automatic weapon killed eight people in a shooting rampage in a town just south of Manila.