PARIS — A 15-month inquiry into the disintegration of Malaysia Airlines Flight 17 in the skies over eastern Ukraine has concluded that the aircraft was most likely attacked from the ground by a Russian-made missile, Dutch air accident investigators said Tuesday.
The findings — based on distinctive metal shrapnel and traces of paint in the bodies of crew members in the cockpit, near where the missile hit — are the most detailed evidence so far from a five-nation investigative team that has retrieved and sifted through several tons of debris and human remains.
"Flight MH17 crashed as a result of the detonation of a warhead outside the airplane above the left-hand side of the cockpit," said Tjibbe Joustra, chairman of the Dutch Safety Board, using a common reference to the flight number. The explosion tore off the forward part of the plane, which broke up in the air. The crash killed all 298 people aboard; the investigation found that many died instantly, while others quickly lost consciousness. "It is likely that the occupants were barely able to comprehend their situation," the board found.
While the findings stop short of assigning responsibility for the crash, a task that has been left to Dutch prosecutors, they appear consistent with a theory widely promoted by the authorities in the United States and Ukraine: that the plane, a Boeing 777, was shot down by Russian-backed separatists armed with an SA-11, or Buk, surface-to-air missile.
Russia has vehemently disputed that theory, and it continued to do so Tuesday with a competing presentation, saying that the missile must have been fired from Ukrainian-held territory and that it was of a type that is no longer found in Russia's arsenal.
The report on the July 17, 2014, crash was presented at the Gilze-Rijen Air Base in the Netherlands. The flight's passengers and crew members came from about a dozen countries, but two-thirds of those on board were Dutch citizens.
The board was sharply critical of the Ukrainian authorities for failing to close the airspace above the conflict zone. It found that 160 civil aviation flights went through on the day of the crash, until the airspace was closed.
"Why was Malaysia Airlines Flight MH17 flying over an area where an armed conflict was taking place?" Joustra asked. "The question was on the minds of many people after the crash. The answer was as straightforward as it is disquieting: Almost all operators were flying over that area. And why? Because nobody thought that civil aviation was at risk."
There was sufficient reason to close the airspace as a precaution, but "the Ukrainian authorities failed to do so," he said.
The team of investigators was led by the Netherlands but included members from four other countries heavily affected by the crash: Australia, Belgium, Malaysia and Ukraine. In addition to what brought down the aircraft, the safety board has examined why the plane was flying over a region in conflict; whether the passengers would have been conscious as the plane went down; and why some relatives had to wait as long as 14 days before getting confirmation that their loved ones were on board.
In addition to studying the causes of the crash, the Dutch report will also identify a number of shortcomings in the systems that governments have in place for communicating risks to commercial airliners when flying over conflict zones.
From the outset, the Russian government has tried to offer alternative versions of what caused the plane to break up over eastern Ukraine.
Initially, the Defense Ministry presented what generals said was radar data indicating that a Ukrainian fighter jet had flown nearby, possibly shooting down the Malaysia Airlines flight. This year, officials with Almaz-Antey, the state corporation that manufactures the Buk anti-aircraft missiles, held a news conference in Moscow to say that they believed one of their missiles had shot down the plane but that an analysis of the angle of impact showed it must have been fired from territory controlled by the Ukrainian army.
To coincide with the Dutch announcement, Almaz-Antey scheduled a news conference Tuesday to reveal the results of what the company said was its own investigation, which it added was an "expensive" experiment in which a Buk warhead was detonated near the fuselage of a passenger jet.
Then, this month, after a Ukrainian security official had suggested in an interview with the Dutch news media that shrapnel removed from the bodies of the victims proved a Buk was to blame, Tass, the Russian state news agency, quoted an independent expert objecting that it was too early to conclude such a missile brought down the plane.
Tass quoted the expert, Ivan P. Konovalov, the director of a Moscow research center, the Center for Strategic Trends, as saying that if the Dutch Safety Board indeed "reaches a firm conclusion that the Boeing was struck by a Buk anti-aircraft rocket, then it should be taken into consideration that at that time only the armed services of Ukraine had these complexes and the People's Republics of Donbas had no such complex systems then or now." He was referring to pro-Russian separatist governments set up in the Donbas region in eastern Ukraine.
The Kremlin has denied any involvement in arming separatist fighters in eastern Ukraine or the shooting down of the Malaysia Airlines flight.
The crash has highlighted concerns among aviation authorities about the risks posed to civilian aircraft by missiles fired from the ground.
Little more than a week after the crash, U.S. and European regulators briefly banned their airlines from flying to and from Ben-Gurion International Airport in Tel Aviv after a missile fired from Gaza landed near it.
The European Aviation Safety Agency recently published a warning to airlines alerting them to the potential risks of flying through portions of Iranian and Iraqi airspace after Russian warships in the Caspian Sea fired cruise missiles into territory held by the Islamic State in Syria.
Nicola Clark reported from Paris, and Andrew E. Kramer from Moscow.