after finding traces in London flat

Ricin was used to assassinate the Bulgarian defector Georgi Markov in London in 1978. He was injected using the point of an umbrella and died within four days. The symptoms of ricin poisoning are similar to flu, including a high temperature and loss of appetite. Hospitals and doctors across the UK have been put on alert for signs of ricin poisoning.

The toxin must be inhaled, ingested or injected to take effect. But it is thought that it would be more difficult to mount a mass attack with ricin than with anthrax or botulinum toxin, for example. New Scientist