"We believe the case is not yet solved because there are three others, whose identities remain unknown," said lawyer Ricardo Diaz, chief of the NBI-International Police.
Diaz said the NBI investigation will be parallel to the police probe, which was apparently concluded.
Diaz said relatives of two of the victims personally sought the help of the NBI to identify, arrest and prosecute the killers.
Despite the request, Diaz said the NBI did not immediately step into the case in deference to the request of PNP regional director Chief Superintendent George Aliño to allow them to handle the investigation.
Now that the main part of the investigation is completed with the filing of charges, Diaz said the bureau can start its own investigation.
"We will go there with an open mind and not necessarily to corroborate the police conclusion," Diaz said. "In case the NBI probe jibes with the police finding, then it would be confirmatory."
NBI Director Reynaldo Wycoco said the bureau has been providing the Philippine National Police (PNP) with technical and forensic assistance in the investigation of the Boracay massacre.