A shot hit Mr. Osmayev on the right side of his chest. But he was not immediately incapacitated and struggled with the shooter for control of the gun. Ms. Okuyeva, however, long fearful of assassination attempts, was carrying a pistol under her coat, as well as a tube of the blood-clotting agent Celox in her purse. She shot Mr. Denisultanov-Kurmakayev four times as he and her husband fought. Both were gravely wounded but survived.“I will always be thankful,” Mr. Osmayev said in an interview of his wife’s quick draw. “Because of her reaction, we are both alive today.”The survival of the assassin could elevate the importance of the case, should investigators obtain his cooperation.In March, a former Russian lawmaker who fled to Ukraine, Denis N. Voronenkov, was gunned down on a sidewalk outside the Premier Palace hotel in Kiev. Mr. Voronenkov’s bodyguard shot and killed the attacker. Last year, a car bomb killed a journalist, Pavel Sheremet, on a central street of the capital, and no arrests were made.After the attack on Mr. Osmayev and Ms. Okuyeva, Ukraine’s Interior Ministry and lawmakers blamed the Russian intelligence services. Ukraine’s SBU intelligence agency, however, has said there is insufficient evidence to determine whether the killer pretending to be a journalist was a Russian agent, but it has not ruled out that possibility.“For the world community, what is important is we have proof Russia is committing terrorist acts in other countries,” said Anton Gerashenko, a lawmaker. “His tongue may loosen to say who sent him here and why,” he said of Mr. Denisultanov-Kurmakayev.