The Joint Investigation Team (JIT) image shows a "Venturi", which emits propellant gases, like a car exhaust.
Dutch prosecutors want more information from Russia about the Buk, which they say killed 298 people aboard Malaysia Airlines Flight MH17 in July 2014.
The West and Ukraine say Russian-backed rebels fired the Buk missile.
Russia argues that Ukrainian forces downed MH17. The Boeing 777, en route from Amsterdam to Kuala Lumpur, crashed in rebel-held territory.
The JIT interim report explains the progress of the criminal inquiry. The experts are studying a mass of tiny fragments retrieved from the crash site.
Last year, a Dutch Safety Board report concluded that MH17 was downed by a Russian-made Buk, but did not say who fired it. Board president Djibbe Joustra said at the time that the rebels were in charge of the area from which it was fired.
Dutch prosecutors plan to present the results of their investigation in the autumn. They say it is at "a very advanced stage".
But the JIT interim report says more technical and operational details about the missile are needed.
The Boeing 777 crashed at the height of the conflict between Ukrainian government troops and pro-Russian separatists.
Some families of the victims are suing Russia and its President, Vladimir Putin, in the European Court of Human Rights.