A variety of methods and techniques for requirements elicitation and analysis have been proposed, in response to the diverse needs posed by the different types of information that have to be managed in designing complex software systems. Experience from real projects gives evidence that often these techniques are combined within a project, but which requirements each technique can better contribute to specify, and which information sources are prevalently used during requirements elicitation and validation is poorly documented. In this paper, we describe a retrospective analysis of the requirements engineering process of a project in the domain of ambient assisted living, where several techniques were used to elicit the requirements of a socio-technical system. By empirically analysing the available project documentation, we collect evidences of the type of information that various elicitation techniques can give in a real project, linking initial sources of information to final requirements through different analysis paths. We illustrate the design of this study and present an analysis of the collected data.