On the morning of Sunday 18 January 1981, a fire broke out at a house in New Cross, London, injuring many, and killing thirteen young Black men, women, and children. In 1983, a fourteenth name was added to the toll. The New Cross massacre, named by activists, quickly became the focal point of a campaign for truth and justice which saw up to 20,000 march across London on the Black People’s Day of Action, and which later extended to the courts. Records of the New Cross Massacre Action Committee, an umbrella organisation, were preserved and curated in an archive at the George Padmore Institute. Using the GPI archive alongside additional archival collections, contemporary newspaper reporting, and cultural artefacts, this chapter examines how bereaved families, survivors, British Black Power activists, and community organisers mobilised experiential expertise to challenge the legal and scientific expertise deployed by state institutions. In doing so, it focuses on three spaces in which experiential expertise was operationalised to improve the welfare of Black Britons: street, courts, and archive. The chapter also reflects on the positionality and ethics of academics researching traumatic experiences of minoritised and marginalised communities when academics themselves do not share those experiences.