Mass shooting in the middle school Vladislav Ribnikar in Belgrade

[FlatAssembler]

"He might have a bias." is not a valid argument to reject a scientific study. You need to prove that he has a bias by doing a better study.

Right, which is why you don't settle for the first "study"/opinion piece coming down the pike as having anything but tentative conclusions. And that doesn't address the other problems. The bottom line is that accepting the only study of a field as more accurate simply because no others have yet been done is idiotic. It's assuming the study is correct in its conclusions, and as we know, or should know as you apparently do not, the onus of evidence is on the claimant.

The burden of proof initially lies on one making the claim. But once the one making the claim provides some proof, the burden of proof switches onto the one who is claiming that proof is wrong.
Think of the Mad Revisionists, the conspiracy theorists who are claiming that the Moon doesn't exist. They claim that the burden of proof is on us who claim the Moon exists, but that's incortect. There is a proof that the Moon exists: we see it. Since they claim there is something wrong with that proof, that the Moon is a hologram, the burden of proof is on them.

Besides, I think that the burden of proof even a-priori lies on those supporting gun control. Gun control is a coercive government policy, and claiming that coercion helps is an extraordinary claim. Extraordinary claim requires extraordinary evidence.