Russian officials and their spokespersons are currently requesting, even demanding that Germany provide Russia with evidence, of any physical or biological kind, which demonstrates the poisoning of opposition activist Alexei Navalny with a Novichok agent. It is worth recalling that the last time such hard evidence was presented regarding an event of potential confrontation of two nuclear powers, was six decades ago — and military confrontation was avoided. That “event” was of course the Cuban Missiles Crisis of 1962.
On Oct. 25, 1962 in a famous UN Security Council session watched by millions of Americans on television, the Soviet Union’s UN Ambassador Valerian Zorin demanded evidence that Soviet intermediate- and medium-range missiles had been placed in Cuba, and said, “Falsity is what the United States has in its hands, false evidence.” American Ambassador Adlai Stevenson, rather than alleging, “We have solid evidence and sources,” and “We could easily and fully demonstrate this with secret evidence,” etc., actually SHOWED photographs to the Security Council and the TV cameras, of the missiles and their batteries. The photographs had cost the life of a U2 pilot and loss of his highly secret plane. As is well known, the United States and Soviet Union were able to resolve the crisis without (likely nuclear) war, and actually to reduce nuclear armaments somewhat.
It could be added that when the United States “quarantined” Cuba during that crisis, President Kennedy ordered that ships approaching Cuba be allowed through the quarantine if the United States had evidence that they were not carrying armaments; and in fact, two ships carrying petroleum products were allowed through before the first Soviet arms-bearing ship turned around.