CNN reports that according to the Russian government a Ukrainian jet was tailing Malaysian Airlines flight MH17 before it was shot down. 

On Monday, Russian officials floated the possibility that a Ukrainian fighter jet might have downed the plane.

Russian monitoring showed a Ukrainian Su-25 fighter jet flying along the same route and within 3 kilometers to 5 kilometers (1.9 miles to 3.1 miles) of Flight 17, Lt. Gen. Andrei Kartapolov of the Russian Army General Staff said at a news conference, Russian state media reported.

"We would like to know why the Ukrainian plane was flying along a civilian route on the same flight path as the Malaysian Boeing," Kartapolov said, according to the reports.

Pro-Russian rebels have also denied responsibility for the shootdown.

In an interview with Cuomo broadcast Monday on CNN's "New Day," the self-declared rebel Prime Minister in Donetsk, Alexander Borodai, said he believed Ukrainian forces either shot the plane down with a surface-to-air missile or, as the Russian general suggested, one of its own fighter jets.

There are a few problems with this theory. First, flight MH17 was shot down five days ago. For five days the evidence has been growing that the separatists, armed with the Buk surface-to-air missile, shot down this aircraft. So why wasn't this claim reported by the Russian government five days ago?

A second problem -- according to the manufacturer of the Su-25, Sukhoi, the maximum altitude of the Su-25 carrying no external ordnance and stores is only 7 kilometers (7000 meters, 23,000 feet). MH17 was flying at 10,000 meters, about 33,000 feet. By this logic, even if the Su-25 was flying directly under MH17 it would be at least 3 kilometers away. How does that fit with the claims that the Russian government is making?

Update - It's been pointed out that the Su-25 can briefly fly higher than 7km because while its service ceiling is 7km it can surge to higher than this, perhaps even 10km. However, all these altitudes are calculated based on an aircraft carrying no missiles or bombs. All of this raises new questions -- if it was Ukraine's design to shoot down a civilian aircraft, why wouldn't they use another aircraft, like the Su-27, which is a far better tool for the job.

Ultimately there is yet another question. If Russia believed on Thursday that Ukraine's airforce was just shooting down civilian aircraft, why didn't they raise the alarm sooner?

We consulted several aviation experts to answer some of these questions, but none of them wanted to go on record for the same two reasons: 1) they believed the claim was ridiculous and 2) they decided that it would bring too much heat from the trolls to go on record.