Academic writing is a complex and cognitively demanding task, which entails that students search, read and critically evaluate a substantial number of sources that are then synthesised and incorporated in the students' own texts. This ability of using sources efficiently is a cornerstone to academic literacy (Cumming et al., 2016), while the way how students handle the sources affects the text quality (Leijten et al., 2019). To our knowledge, research on the use of sources in writing longer authentic academic texts over an extended period of time is scarce (cf. Ivanov et al., 2022). The aim of this paper is to analyse what kind of, when and how digital sources are used in the process of writing a graduate thesis (15 ECTS) in the teacher education programme. We also trace how individual sources are used through the writing process and how it shapes the final text product. The data was collected using a keystroke logging software (Inputlog), that recorded all events on the participant's laptop in 62 writing sessions of approximately 258 hours over 9 weeks. The recording was administered by the participating student, a 46-year-old female, at the end of her education for primary school teacher. The in-built function of Inputlog was used to analyse the data quantitatively to provide a picture of when and to which extent the student used digital sources, while manual qualitative analysis was used first to categorise the sources and establish at what stage of the text production they were consulted and then to reveal how these individual sources were incorporated in the student thesis. The results show how digital sources are used to compose the body of the thesis as well as to monitor the writing process and revise the thesis. The results may inform the instruction in literature searching and referencing while writing a graduate thesis as well as contribute to students' awareness of how digital sources can be efficiently used.