Police are now determining whether the victim, Fe Docuyanan, was raped because she was found naked.
Senior Superintendent Francisco Uyami Jr. Pasig City police chief said they have invited for questioning three male boarders of the two-storey apartment, located at 4215 Saint Paul Street, SPS Subdivision, Barangay Rosario.
Docuyanan had previously complained to her sister, Grace, that the three male boarders were peeping on her everytime she changed clothes in her room.
"We already summoned the three male boarders to shed light to the incident. They are scheduled to appear before police investigators," Uyami told an interview.
The three male boarders stay in a house adjacent to the apartment.
Uyami said Grace discovered her younger sisters body when she arrived home from work at about 7:45 p.m. last Monday.
An initial investigation conducted by Senior Inspector Lorenzo Trajano, the local police criminal investigation unit head, found signs of struggle from the sala to the toilet as indicated by bloodstains on the floor.
"The victim fought back but it appears that her attackers were strong," Trajano said. The young Docuyanan was stabbed four times in the body.
An initial report submitted by crime scene analysts stated that fluid believed to be semen was found in the apartment, bolstering police suspicions of rape. Samples were taken for further analysis.
Trajano said the Docuyanan sisters occupied one of the upper rooms of the apartment while the three male boarders lived in one of the rooms downstairs.
The boarders room was already vacant before Docuyanans body was discovered, according to a police investigator.
The police are also not ruling out robbery as the motive in the killing because the Docuyanan sisters mobile phones, altogether worth P9,000, were reported missing.