The radiation expert who discovered the poison that killed Alexander Litvinenko "committed suicide" by stabbing himself repeatedly with two knives months after a trip to Russia, a coroner ruled. Matthew Puncher, 46, bled to death at his home after receiving multiple stab wounds across his body from two kitchen knives, an inquest heard. A pathologist said he could not completely exclude the possibility that someone else had been involved in the death of the father, but came to the conclusion that the injuries were self-inflicted.