'So, as you agree, they are in the habit of shooting down planes as and when the opportunity arises and they have suitable weapons in the right place.'
Yes, they try to shoot down planes that are bombing them, but they have never been able to shoot a plane at 33000 feet because they don'have the weapons to do so and even Yats, Poroshenko and all the rest of them refer to the rebels as "drunken gorillas" who are not able to operate such sophisticated weapons.
I agree that there are Russians fighting there. The leader, Stelkov himself, is a Russian, but they are volunteers and Russia has not sent thousands of troops in.
I think that Yats and Poroshenko and some others want the Russians to admit they did it. Yats and the rest don't say that the "drunken gorillas" did it, they upfront say that the Russians did it. Whoever did it, we assume it was a mistake, so if the Russians are found to have done it, then maybe Putin will admit that a mistake was made. The Ukrainians made a mistake in 2001 and shot down a Russian airliner and the Americans made a mistake and shot down an Iranian airliner once.
I don't think the Russians will be found to have made a mistake, but we will have to wait and see for the results of the inquiry. It is possible that they did do it.