The final part of the boarding schools investigation ordered by Interior Secretary Deb Haaland in 2021 has been released at:
https://www.bia.gov/sites/default/files/media_document/doi_federal_indian_boarding_school_initiative_investigative_report_vii_final_508_compliant.pdf
The first part is at: https://www.bia.gov/sites/default/files/dup/inline-files/bsi_investigative_report_may_2022_508.pdf
The WaPo article includes results that were part of its own investigation.