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Open-Source Evidence & the Laws of War
- The Reports

Online open-source investigations (OOSI) are increasingly used in documenting the conduct of war and violations of international law. Alongside other, established, methods of evidence gathering, OOSI is empowering both local and transnational actors in their efforts to both analyse and use open-source materials for accountability.


On 24th October 2022, GLAN and Bellingcat released two reports that seek to answer two key questions: can OOSI help in documenting and analysing violations of the law applicable in war (international humanitarian law or IHL); can open source information serve as evidence in a war crimes trial?


The reports are the product of a four year collaboration between Bellingcat and GLAN, and draw their analysis from our common work documenting and analysing the aerial bombardment campaign of the Saudi-led Coalition in the war in Yemen.

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Open-Source Video as Legal Evidence

This report provides an account of a mock hearing under the jurisdiction of English law, in February and March 2021 on the admissibility of an open-source video depicting the aftermath of a Saudi/UAE-led coalition airstrike in Yemen and the impact of a second attack.




Open-Source Investigations & The Laws of War

This report is the product of sustained analysis of online open-source investigations on airstrikes in Yemen from the point of view of IHL, supported by members of the Advocates for Human Rights at Harvard Law School. 

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Online open-source investigations (OOSI) can lead to admissible evidence in criminal proceedings. It can advance independent determinations on compliance with the IHL principles of distinction and proportionality in targeting – a notoriously difficult task which typically occurs without access to classified information from the attacking forces.


Our reports clarify and inform on both the usefulness as well as the limitations of OOSI in the process of documenting, analysing and using open-source evidence for accountability purposes. They will be of use and further empower local and transnational actors.

Watch GLAN and Bellingcat present on the launch of two reports on open-source information as evidence for international accountability

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The journey behind the development of the reports

An expert workshop convened by GLAN considered the potential for digital evidence to be used as evidence in legal proceedings. This resulted in a draft methodology for open source investigators one that struck a balance between being practical as well as robust.


To test and further refine the methodology an interdisciplinary “Hackathon” event was convened with objective of using the methodology while investigating alleged airstrikes in Yemen. The results of these investigations were subsequently published.



GLAN and Bellingcat continued to revise the methodology during the completion of further investigations into attacks causing grave civilian harm in Yemen.

A mock trial is convened to test our methodology in the context of an English court.

Justice and Accountability Unit launched with Bellingcat and methodology applied to online open-source investigations on Ukraine. Two reports launched.



Expert convening 




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Mock Trial





Harnessing User-Generated Content in Accountability Efforts for International Law Violations in Yemen | Opinio Juris | 19 December 2019

How Global Legal Action Network is documenting digital evidence of airstrikes against civilians in Yemen | Huridocs | 12 November 2019

The Yemen Project: Open Source Investigations and the Law of War | Just Security [United States] | 23 September 2019

The Race to Archive Social Posts That May Prove Russian War Crimes | Wired Magazine | 11 April 2022

Ukraine: Online posts 'transform' war crimes documentation | BBC News | 17 April 2022


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