  Crowdsourced investigations shore up democratic institutions by debunking
misinformation and uncovering human rights abuses. However, current
crowdsourcing approaches rely on simplistic collaborative or competitive models
and lack technological support, limiting their collective impact. Prior
research has shown that blending elements of competition and collaboration can
lead to greater performance and creativity, but crowdsourced investigations
pose unique analytical and ethical challenges. In this paper, we employed a
four-month-long Research through Design process to design and evaluate a novel
interaction style called collaborative capture the flag competitions (CoCTFs).
We instantiated this interaction style through CoSINT, a platform that enables
a trained crowd to work with professional investigators to identify and
investigate social media misinformation. Our mixed-methods evaluation showed
that CoSINT leverages the complementary strengths of competition and
collaboration, allowing a crowd to quickly identify and debunk misinformation.
We also highlight tensions between competition versus collaboration and discuss
implications for the design of crowdsourced investigations.
