Researchers and developers have suggested that the use of diegetic interfaces can enhance users' sense of presence and immersion in virtual reality (VR) applications. While concepts of diegetic interfaces in VR are analogous to those seen on 2D displays, little work has considered how they might integrate with the movement-based controllers commonly used in consumer VR systems, to create higher fidelity interactions. In this paper we present a study (N = 58) in which we compare participants' experiences of diegetic and non-diegetic tool management interfaces, in a prototype VR crime scene investigation (CSI) training application. Contrary to expectations, we do not find evidence that participants' sense of presence is elevated when using the diegetic interface; however, we suggest that this may be due to reported higher levels of perceived workload, which can act to degrade user experience and engagement. We conclude by discussing the relationship between diegetic interface design and interaction fidelity, and highlighting trade-offs between fidelity, engagement, and learning outcomes in VR training applications.