It doesn't matter. The source of the claims is the Russian government. That automatically discredits it in the minds of liberals whether it's Russian media, Chinese, Turkish, or French.

Especially since the entire west has been going suspiciously hard from day one on "this was ISIS-K, no one else, Ukraine is not involved" being repeatedly parroted with the subtext that any suggestion otherwise is Russian propaganda and excusing escalation towards Ukraine. Day two they were already accusing Putin of using the attack to justify an increased response to Ukraine and calling it crazy.

It's unfalsifiable. If the Russians say it then they're liars because they're Russians and evil Putin is a dictator who maybe did it himself to get at Ukraine or something for some reason. If a western source says it they're Russian agents, been duped by Russia, are doing Russia's dirty work. There is no win here if you're trapped in the liberal paradigm of the aggressor Russians and Putin as a modern Hitler.

The sources for the investigation into the money are not going to be something open source intelligence can discern, you're not going to likely have reporters able to get access to trace money the way a government intelligence agency can so by its nature it's what government do you trust.

All you can do is point to people with ISIS patches pictured in Ukraine. Can point to old stories about Turkey opening a corridor for fighters (including ISIS but not usually mentioned) to go from Syria to Ukraine to fight Russians. Can point to the inconsistencies in this attack's methods of operation and past ISIS and islamic extremist tendencies and point to the Ukrainian regime's history of targeting civilians in drone attacks even deep in Russia. All things liberals will brush aside and deny.