1. Appeal Court of Varna. 2021. Varnenskiyat apelativen sad potvardi prisadata po delopo “Hitrino”. https://varna-as.justice.bg/bg/news1/15997 (accessed 29 June 2022).
2. Archive of Institute of Ethnology and Folklore Studies with Ethnographic Museum, Bulgarian Academy of Sciences (AIEFSEM – BAS), № 1058-III. Terenni materiali na tema “Vlakovata katastrofa v s. Hitrino, Shumensko.” Sabrani v perioda 2018 – 2019 g. v s. Hitrino, Shumensko ot Y. Erolova.
3. Archive of Institute of Ethnology and Folklore Studies with Ethnographic Museum, Bulgarian Academy of Sciences (AIEFSEM – BAS), № 1064-III. Terenni materiali na tema “Vlakovata katastrofa v s. Hitrino, Shumensko.” Sabrani v perioda 2018 – 2019 g. v s. Hitrino, Shumensk ot Pl. Stoyanova.
4. Archive of Institute of Ethnology and Folklore Studies with the Ethnographic Museum, Bulgarian Academy of Sciences (AIEFSEM – BAS), № 1065-III. Terenni materiali na tema “Vlakovata katastrofa v s. Hitrino, Shumensko.” Sabrani v perioda 2018 – 2019 g. v s. Hitrino, Shumensko ot Y. Erolova.
5. Archive of Institute of Ethnology and Folklore Studies with Ethnographic Museum, Bulgarian Academy of Sciences (AIEFSEM – BAS), № 1111-III. Anketi na tema “Vlakovata katastrofa v s. Hitrino, Shumensko.” Sabrani v perioda 2018 – 2019 g. v s. Hitrino, Shumensko. Sabrani ot M. Maeva, Pl. Stoyanova, St. Kanev and Y. Erolova.