Contribution structures offer a way to model the network of people who have participated in the requirements engineering process. They further provide the opportunity to extend conventional forms of artifact-based requirements traceability with the traceability of contributing personnel. In this paper, we describe a case study that investigated the modeling and use of contribution structures in an industrial project. In particular, we demonstrate how they made it possible to answer previously unanswerable questions about the human source(s) of requirements. In so doing, we argue that this information addresses problems currently attributed to inadequate requirements traceability.