Nerve Agent Found In U.K. Is Rare And Definitely Russian

Nerve Agent Found In U.K. Is Rare And Definitely Russian
Military personnel wearing protective suits investigate the poisoning of Sergei Skripal in Salisbury, England. Skripal and his daughter, Yulia, remain critically ill.

Novichok-class agents were developed in top-secret Russian labs at the end of the Cold War. Experts say only Russia is known to have made them. "They've been a deep, dark secret," says one expert.

(Image credit: Chris J Ratcliffe/Getty Images)