No matter how hard Russia and its Syrian allies try to deny their involvement in the chemical weapons attack on Idlib, all the available intelligence shows they were directly responsible for committing a war crime.
While categorical evidence is always hard to acquire in an active warzone like Syria, intelligence officials in the US and Britain believe there is already sufficient material available to blame the atrocity directly on the Assad regime and its Russian protectors. A regime warplane was identified operating in the area at the time the attack took place.
Moreover, the aircraft was operating in air space controlled by the Russian military, which has been instrumental in turning the tide of the Syrian conflict in Bashar al-Assad's favour in recent months.
By the time the truth is finally established, the international agenda will have moved on, and the likelihood of retaliatory action being taken will be diminished.
The Assad regime will also have drawn encouragement from former US President Barack Obama's failure to follow through on his threat to launch military action after it carried out another chemical weapons attack on its own citizens on the outskirts of Damascus in 2013.
The other intriguing question concerns why Russian President Vladimir Putin allowed the Assad regime to carry out the attack in the first place.
The Russians have detailed knowledge of the regime's chemical weapons stockpiles because the Russian military has spent the past 30 years helping the Syrians to develop their own weapons of mass destruction.
Moreover, it is the Russians that keep the Syrian warplanes flying as a result of the regular supplies of aviation fuel that Moscow regularly delivers to Damascus.
But Putin has nevertheless taken a big gamble by supporting the Syrian regime's attack on Idlib.
On Monday he received a personal telephone call from US President Donald Trump, who offered his commiserations for the terrorist attack on the St Petersburg underground.
As Trump has frequently indicated he wants to improve relations with the Kremlin, this presented Putin with a good opportunity to improve on his fraught relationship with the White House.
Instead, the Russian leader has opted to support the Assad regime's decision to intensify hostilities in Syria, which is no doubt Putin's way of testing the Trump Administration's mettle, to see whether it has the resolve to deal with countries accused of committing war crimes.
Mr Putin may well find that, this time, he has overplayed his hand.
Trump may have given out conflicting signals about the type of relationship he would like with the Kremlin.
However, hardened Cold War veterans such as Defence Secretary James Mattis and National Security Advisor General HR McMaster are unlikely to be taken in by the Russian leader's duplicity.