"We assess Malaysia Airlines Flight 17 … was likely downed by a surface-to-air missile, an SA-11, operated from a separatist-held location in Eastern Ukraine," Samantha Power, U.S. ambassador to the United Nations, said at an emergency meeting of the U.N. Security Council.
She added that investigators "cannot rule out technical assistance from Russian personnel."
According to the Times, Buk missiles were first manufactured in the 1970s. The 18-foot-long missiles can sometimes reach heights of up to 70,000 feet, far higher than the 33,000 feet that Flight 17 was believed to be flying at. They are typically operated by two-vehicle units, one being used for targeting, but can be operated by a single vehicle.
If the rebels were to blame for the strike, how they could have come into possession of such weaponry and operated it is likely to be one of the most pressing questions in the investigation of the Flight 17 crash.
The Associated Press reported two possibilities Thursday. Experts told the news agency that the Ukrainian military might have abandoned equipment while retreating from positions in eastern Ukraine. But it has also been speculated that the rebels could have received anti-aircraft artillery from the Russian military.
U.S. military officials have accused the Russians of providing anti-aircraft weapons to the rebels, according to the New Republic. Russian officials have countered that the rebels seized control of any such weaponry on their own.
"The equipment had to come from Russia" if separatists fired the missile, former Secretary of State Hillary Clinton said Thursday. "What more the Russians might or might not have done, we don't know.”
There have also been unverified reports of rebels smuggling a Buk missile launcher out of Ukraine and into Russia following the crash, according to The Telegraph in London. The Ukrainian government released a video Friday that purportedly depicted the unit on the move.
As for why rebels would shoot down a commercial plane, one defense expert provided a possible explanation to the AP. Larry Johnson, a former CIA official, said that the Buk missile system is sophisticated and difficult to operate.
When using its targeting system, he said, the rebels could have seen a dot on their radar and not known what it was. They have already reportedly targeted and shot down Ukrainian military aircraft in recent weeks.
"These aren't highly trained FAA air traffic controllers," Johnson said. "You're tracking something on radar, you see a dot, you get confused. I don't think it was deliberate. I think it was mistaken identity."
Pictured: Russian air defense missile system Buk-M2 is on display at the opening of the MAKS Air Show in Zhukovsky outside Moscow on Aug. 27, 2013.