In earlier work, we have introduced Secure Tropos, a requirements engineering methodology that extends the Tropos methodology and is intended for the design and analysis of security requirements. This paper briefly recaps the concepts proposed for capturing security aspects, and presents an implemented graphical CASE tool that supports the Secure Tropos methodology. Specifically, the tool supports the creation of Secure Tropos models, their translation to formal specifications, as well as the analysis of these specifications to ensure that they comply with specific security properties. Apart from presenting the tool, the paper also presents a two-tier evaluation consisting of two case studies and an experimental evaluation of the tool’s scalability.