MH17 crash: Did Russia pull the trigger? Ukraine says yes

Kiev, Ukraine (CNN) -- Did a Russian fire the missile that downed Malaysia Airlines Flight 17? That depends on who you ask.

A top Ukrainian official says he has no doubt.

Vitaly Nayda, Ukraine's director of informational security, told CNN the person who shot down the flight was "absolutely" a Russian. "A Russian-trained, well-equipped, well-educated officer ... pushed that button deliberately," he said.

"We taped conversations" between a Russian officer and his office in Moscow, Nayda said. "We know for sure that several minutes before the missile was launched, there was a report" to a Russian officer that the plane was coming, he said.

"They knew the plane was coming with constant speed, in constant direction," and should have known it was not a fighter jet but "a big civilian plane," he said.

Does debris prove MH17 was shot down? Who leads the pro-Russian rebels?

U.S. officials say pro-Russian rebels were responsible for shooting down Malaysia Airlines Flight 17, but they now believe it's likely the rebels didn't know the plane was a commercial airliner when they opened fire, U.S. intelligence officials said Tuesday.

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The officials have determined that Russia bears some responsibility for the incident because of its support for the rebels, but they haven't been able to determine exactly who fired the missile, whether Russian military were at the site or whether the Russians were directly responsible for launching the missile.

Moscow has denied claims that it pulled the trigger. And Russian Army Lt. Gen. Andrei Kartapolov suggested a Ukrainian jet fighter may have shot the plane down.

Ukrainian President Petro Poroshenko rejected that in an exclusive interview with CNN, saying that all Ukrainian aircraft were on the ground at the time.

Vitaly Churkin, Russia's ambassador to the United Nations, was asked Monday about different intercepted recordings, purportedly of pro-Russian rebels talking about shooting down a plane. Churkin suggested that if they did, it was an accident.

"According to them, the people from the east were saying that they shot down a military jet," he said. "If they think they shot down a military jet, it was confusion. If it was confusion, it was not an act of terrorism."

Pro-Russian rebels have repeatedly denied responsibility for the attack.