On 7 September Markov was stabbed in the back of his right thigh with an umbrella while waiting at a bus stop on Waterloo Bridge. The pellet measured 1.70 mm in diameter and was composed of 90% platinum and 10% iridium. It had two holes with diameters of 0.35 mm drilled through it producing an X-shaped cavity. A sugary substance coated the tiny holes creating a bubble which trapped the ricin inside the cavities. The specially crafted coating was designed to melt at 37° C. After the pellet was shot into Markov the coating melted and the ricin was free to be absorbed into the bloodstream and kill him. Regardless of whether the doctors treating Markov had known that the poison was ricin the result would have been the same as there was no known antidote to ricin at the time.