Jonathan Frederic De Santos

National Bureau of Investigation Senior Agent John Mark Calilung testifes at the Senate impeachment court on July 7, 2026 on his forensic examination of videos of Vice President Sara Duterte. Mara Tan, ABS-CBN News

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ABS-CBN Research and Verification Unit

<div><span class="fr-img-caption fr-fic fr-dib" style="width:960px;display:block" width="960"><span class="fr-img-wrap"><img src="https://od2-image-api.abs-cbn.com/prod/editorImage/1783923682895calilung.jpg" style="width:960px" class="fr-fic fr-dib" width="960"/><span class="fr-inner" style="text-align:left">National Bureau of Investigation Senior Agent John Mark Calilung testifes at the Senate impeachment court on July 7, 2026 on his forensic examination of videos of Vice President Sara Duterte. Mara Tan, ABS-CBN News</span></span></span></div><p>MANILA — The first witness to take the stand in the<a href="https://www.abs-cbn.com/news/sara-duterte-impeachment-trial"> impeachment trial of Vice President Sara Duterte</a> was John Mark Calilung, a 31-year-old senior agent of the National Bureau of Investigation (NBI).</p><p>Calilung took the stand on the second and third days of the trial, July 7 and 8, to answer questions related to the fourth Article of Impeachment on grave threats and inciting to sedition.</p><p>Article IV alleges that Duterte committed grave threats against President Ferdinand Marcos Jr., First Lady Liza Marcos, and former House Speaker Martin Romualdez and incited sedition through her public statements during livestreamed press conferences.</p><div><a href="https://www.abs-cbn.com/news/sara-duterte-impeachment-trial">Impeachment Trial of Sara Duterte </a></div><p>The prosecutors argue that these acts constitute an impeachable offense.</p><p>Calilung was the agent on the case of the Vice President&#x27;s controversial remarks. His responsibilities included gathering, authenticating, and analyzing digital evidence, preparing official transcripts of the statements, and documenting witness accounts related to Duterte&#x27;s alleged threatening remarks.</p><div><a href="https://www.abs-cbn.com/news/nation/2026/7/7/impeachment-court-tackles-duterte-s-alleged-threat-vs-marcos-1513" rel="noopener noreferrer" target="_blank">Impeachment court tackles Duterte&#x27;s alleged threat vs Marcos</a></div><div><br/></div><div><strong>NBI CAREER </strong></div><div><br/></div><p>Calilung has served at the NBI since 2021 or for five years, and was recently appointed Investigation Agent IV, equivalent to a senior agent, in June 2026.</p><p>Before joining the NBI in 2021, Calilung earned a degree in accounting technology. He also earned a degree in accountancy from Dr. G. Lacson College in Nueva Ecija and passed the Certified Public Accountant (CPA) licensure exam in 2017.</p><p>During the trial, Calilung said he joined the NBI in 2021 as a special investigator.</p><p>In 2022, he was assigned to the Digital Forensic Laboratory Division, where his work involved identifying, preserving, collecting, analyzing, and presenting digital evidence in court.</p><p>He said he was transferred to the NBI Cybercrime Division in 2024, where he investigated violations of the Cybercrime Prevention Act.</p><p>When he investigated the case on Duterte in November 2024, he was three years into his tenure and was serving as Investigation Agent I.</p><p>In April 2026, he said he was assigned to the Cybercrime Investigation and Assessment Center, and two months later, he climbed the ranks to Investigation Agent IV.</p><div><br/></div><div><strong>TRAINING AND EXPERIENCE </strong></div><div><br/></div><p>Calilung testified that he has two years of experience conducting digital forensic examinations and has appeared in court at least 30 times as part of his work.</p><p>Calilung said he learned all the aspects of investigation at the NBI Academy before serving at the bureau. Over the next years, he said he completed training in mobile forensics, computer forensics, and photo and video authentication, which made him certified in computer hacking and digital forensic investigation.</p><p>Calilung mentioned completing a 480-hour cybersecurity training program focused on cybercrime investigation and attending a two-week digital forensics course conducted by Maxcor Inter-Ventures Co. in July 2022. He said this two-week course trained him how to handle and present digital evidence to ensure admissibility in court.</p><p>Calilung also mentioned a five-day digital forensics program in Strasbourg, France and local seminars conducted by the International Criminal Police Organization, or Interpol.</p><div><a href="https://www.abs-cbn.com/news/nation/2026/7/13/-a-threat-is-a-threat-what-to-expect-on-day-4-of-vp-sara-impeachment-trial-0754">&#x27;A threat is a threat&#x27;: What to expect on day 4 of VP Sara impeachment trial </a></div><div><br/></div><div><strong>ROLE IN DUTERTE PROBE </strong></div><div><br/></div><p>Calilung was assigned to investigate Duterte&#x27;s remarks on November 23, 2024, the same day the online press conference was livestreamed.</p><p>He said the investigation began after he received a phone call from his executive officer, who informed him about the online press briefing containing statements classified as threats and directed him to investigate the case.</p><p>The investigation focused on two public events involving Duterte.</p><p>The first was an online press conference livestreamed on former presidential spokesperson Harry Roque&#x27;s Facebook page on November 23, 2024.</p><p>During the online press conference, Duterte said she had arranged for a person to kill Marcos, his wife, and his cousin, former House speaker, should an alleged plot against her life succeed.</p><div><a href="https://www.abs-cbn.com/news/nation/2024/11/26/sara-duterte-faces-subpoena-over-kill-plot-vs-marcos-vp-says-threat-a-plan-without-flesh-1230" rel="noopener noreferrer" target="_blank">Sara Duterte gets subpoena over kill plot vs Marcos; VP says threat a ‘plan without flesh’ </a></div><p>Calilung said the NBI also conducted an open-source investigation to determine whether Duterte had made similar statements before.</p><p>This led them to an earlier online press briefing streamed on the Office of the Vice President&#x27;s official Facebook page on October 18, 2024, where Duterte spoke about imagining beheading and strangling Marcos. The NBI included those remarks as part of its investigation.</p><div><a href="https://www.youtube.com/watch?v=oesA0sB18Io" rel="noopener noreferrer" target="_blank">&#x27;I imagined myself cutting his head&#x27;: Sara Duterte on &#x27;toxic&#x27; relationship with Bongbong Marcos</a></div><p>As part of the investigation, Calilung said he first sent a preservation request to Meta Platforms Inc., owner of Facebook, to preserve the said two Facebook livestreams as digital evidence.</p><p>He then used Open Broadcaster Software (OBS) to create screen recordings of the videos and manually compared them with the original Facebook livestreams to verify that the copies were accurate and had not been altered.</p><div><br/></div><div><strong>QUESTIONS OVER TWO AFFIDAVITS   </strong></div><div><br/></div><p>During cross-examination, defense counsel Carlo Joaquin Narvasa questioned why the NBI submitted two affidavits and whether the first one was sufficient to support the complaint against Duterte.</p><p>The defense presented a Department of Justice (DOJ) certification dated February 5, 2025, which found the NBI&#x27;s original January 30, 2025 referral for preliminary investigation insufficient and recommended further case buildup.</p><p>The DOJ identified seven deficiencies, including the absence of recordings from Duterte&#x27;s October 18, 2024 press briefing, missing affidavits from journalists who witnessed the events, and the lack of a physical USB device containing the evidence.</p><p>Narvasa also said that the president, first lady, and then-House speaker did not personally file complaints or execute affidavits, leaving the NBI the sole complainant.</p><p>Calilung said the NBI addressed these concerns in a revised Joint Affidavit of Investigation dated February 10, 2025, which included additional affidavits and supporting documents.</p><p>He also said that under NBI procedures, the bureau could investigate and file a complaint even without affidavits from the alleged victims.</p><p>Calilung said the revised filing was later found sufficient for a preliminary investigation on February 14, 2025.—<strong><em>Ciara Annatu and Rowena Caronan, ABS-CBN Research and Verification Unit  </em></strong></p><div><strong><em></em></strong><a href="https://www.abs-cbn.com/news/nation/2026/7/13/live-updates-vice-president-sara-duterte-s-impeachment-trial-day-4-1358">LIVE UPDATES: Vice President Sara Duterte&#x27;s Impeachment Trial (Day 4) </a><br/><a href="https://www.abs-cbn.com/news/nation/2026/7/12/escudero-vows-impeachment-process-to-be-faster-in-coming-weeks-1814">Escudero vows impeachment process to be faster in coming weeks </a></div><div><span class="fr-video fr-deletable fr-fvc fr-dvb fr-draggable" contenteditable="false" draggable="true"><iframe width="640" height="360" src="https://www.youtube.com/embed/mPGAXK-K1Ns?&amp;wmode=opaque&amp;rel=0" frameBorder="0" allowfullscreen="" class="fr-draggable"></iframe></span><br/></div>

<p>The first witness to take the stand in the impeachment trial of Vice President Sara Duterte was John Mark Calilung, a 31-year-old senior agent of the National Bureau of Investigation (NBI).</p>

The first witness to take the stand in the impeachment trial of Vice President Sara Duterte was John Mark Calilung, a 31-year-old senior agent of the National Bureau of Investigation (NBI).

Who is John Mark Calilung, the first witness in Sara Duterte’s impeachment trial?

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Who is John Mark Calilung, the first witness in Sara Duterte’s impeachment trial?

ABS-CBN Research and Verification Unit

Published July 13, 2026 02:41 PM PHT

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