The shooting was witnessed by two young girls, aged 12 and 14, the police said.
Investigator PO2 Jorge de la Cruz said victim Marlon Dacara, 31, sustained five bullet wounds in the body.
De la Cruz said Isidro Sauza, junkshop owner and Dacaras boss, looked up the victim in his house with a gun in his hand.
He found Dacara and confronted him about a long-standing debt and demanded payment.
Dacara was shot when he tried to argue his case. Witnesses said Sauza casually left the scene. He remains at large.
Dacara was brought by neighbors to the Pagamutang Bayan ng Malabon died before they got there. Jerry Botial, Ian Estrada