Dear Ms. Justo,
Thank you for posting your request on History Hub!
If the US government received any information about the incident, there may be records of it in the Subject-Numeric Files, 2/1/1963 - 1973; Subject Files, 1967 - 1975; Human Rights Country Files, ca. 1974 - 1978 (documenting 1965 - 1978); Records Relating to Cultural and Human Rights Affairs, 8/25/1954 - ca. 1970; or other series in the General Records of the Department of State (Record Group 59). For more information about these records, please contact the National Archives at College Park - Textual Reference (RDT2) at Archives2reference@nara.gov.
If the information was reported to the President of the United States, there may be records at the Lyndon Baines Johnson Presidential Library. To submit an inquiry, please email them at Johnson.Library@nara.gov.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT2 and the LBJ Library. We apologize for this inconvenience and appreciate your understanding and patience.
For Central Intelligence Agency intelligence reports and analysis, we suggest that you review the CIA Freedom of Information Act Electronic Reading Room and the CIA Records Search Tool (CREST).
Also, you may wish to submit a Freedom of Information Act request to the Department of State and the Central Intelligence Agency for any records still in their custody which have not been released yet.
For information from the Philippine government, you may wish to contact the National Historical Commission of the Philippines, the National Archives of the Philippines, and any other relevant government departments. There also may be other sources of information such as local governments, oral histories, etc.
We hope this is helpful. Best of luck with your research!