A stunning update on Friday afternoon from the Associated Press said the Pentagon is investigating possible Russian participation in the Syrian regime’s chemical weapons attack.

These officials also supported the dire suspicion that nearby hospitals were attacked to cover up evidence of the WMD deployment:

The officials say Russia has failed to control the Syrian government’s use of chemical weapons. They say a drone belonging either to Russia or Syria was seen hovering over the site of the chemical weapons attack Tuesday after it happened. The drone returned late in the day as citizens were going to a nearby hospital for treatment. Shortly afterward, officials say the hospital was bombed. The officials say they believe the hospital attack may have been an effort to cover up evidence of the attack. The officials weren’t authorized to speak publicly on the matter and demanded anonymity. They say they’re still reviewing evidence.

According to CNN, the Pentagon is particularly interested in whether a Russian warplane actually conducted the bombing run on the Khan Sheikhoun hospital where victims were receiving treatment within hours of the attack, “with the aim of destroying evidence.”

Such an inquiry will not, of course, sit well with Russia, which is currently demanding a U.N. Security Council investigation of American aggression.

There have been conflicting reports about whether any Russian personnel or aircraft, particularly helicopters, were present at the Sharyat airbase. Videos can be found online purporting to show Russian helicopters at the base as recently as February, but Fox News quotes Pentagon briefers stating “no Russian aircraft were at the Sharyat airfield” when the missiles struck.

However, the Fox News report also quotes U.S. officials who said “between 12 and 100 Russian military personnel” were present at the base, complete with their own barracks, which the U.S. “took pains” to avoid blowing up. If the chemical weapons attack on Idlib province was indeed conducted from the base, it would be very difficult for the Russians to argue they were unaware a war crime was in progress under their noses.