Were there any people killed by a cassowary?

Yes, but this is not common. The only recorded story of someone being killed by a cassowary occurred back in 1926, when a teenage boy attempted to attack a cassowary with a club, but was kicked to the ground then slashed in the neck by the bird. He died shortly afterwards from a haemorrhaging vein. However, every year in the Australian state of Queensland, there are incidents of injury to people (and also dogs) as a result of encounters with cassowaries.