MOSCOW—After one of Russia’s best-known bankers dropped into a coma in 1995 and died three days later, prosecutors called it a hit by criminals who sprinkled his office telephone with a poison reportedly obtained from a little-known government laboratory.
Now the U.K. says a substance known as Novichok, once made at the same laboratory, put Russian double agent Sergei Skripal and his daughter into a coma in southwestern England. U.K. Prime Minister Theresa May this week blamed Moscow for the attack, which has plunged British-Russian...