I think the answer is: there would be no reason to think that about Putin.
Having said that, a disclaimer (AKA "my bad") is probably in order. The NEXTA twitter post states "Phosphorus shells are prohibited by the Geneva Convention."
This is not actually correct.
>>>The use of white phosphorus is not outright banned under international weapons law.
It is not illegal for militaries to possess it, and armed forces around the world (including U.S. troops) have said they use it to mark a target or create a smokescreen, according to David E. Johnson, a military expert with the Rand Corp.
But like all weapons, it is illegal to use against civilian targets, and the use of air-dropped incendiary weapons in populated areas is prohibited under Protocol III, Johnson said.
“Going after civilian targets indiscriminately is the biggest war crime there is, no matter what the weapon,” he said.<<<
https://www.nbcnews.com/news/world/what-is-phosphorus-bomb-russia-ukraine-rcna21371
Here's a blog post that goes into more detail.
>>>White phosphorus munitions are per se a lawful weapon that can be used against the enemy consistent with the normal
laws of targeting. However, white phosphorus munitions, like any lawful weapon, can be used in numerous unlawful manners,
such as to specifically target civilians or launch attacks indiscriminately. Focusing on the weapon, and not how it is being used, muddies the law and facts surrounding the circumstances in which a war crime may have occurred.<<< (emphasis added)
Focusing on the weapon, and not how it is being used, muddies the law and facts surrounding the circumstances in which a war crime may have occurred.
www.lawfareblog.com
The lawfare blog post states that >>>White phosphorus is often
incorrectly labeled as an “incendiary weapon” or a “
chemical weapon.” Under the LOAC, it is legally neither.<<<
I'm not sure that this assertion is settled law. Either way, there have been reports of Russians using actual incendiary munitions in Ukraine:
>>>Despite some reporting to the contrary, the 9M22S does not deliver a white phosphorous payload. In fact, white phosphorous—whilst available in ‘unitary’ format munitions for incendiary use and sometimes used as an ignition source in some incendiary munitions due to its pyrophoric characteristics, is most often used for marking and screening purposes, dues to the large volume of dense, white smoke it can quickly produce. Magnesium- and thermite-based incendiary munitions, by contrast, are most often used to ignite fires in areas such as fuel depots, ammunition storage sites, and other flammable military targets.<<<
N.R. Jenzen-Jones Editor's Note: This article draws, in part, on a previous ARES article examining the use of the 9M22S incendiary rocket in eastern Ukraine in 2014. Images shared by ABC News foreign correspondent James Longman via social media earlier today (19 April 2022) show the remnants of...
armamentresearch.com
It's not clear to me if the NEXTA video shows WP or some other incendiary munitions.
It wouldn't surprise me if the Russians are committing war crimes by targeting civilians and/or launching attacks indiscriminately, but it's not accurate to say that phosphorus shells, by themselves, are prohibited by the Geneva Convention.
