Your OC gas link seems broken.

@Lag Sorry, it's geo-restricted. Here's a tweet by the author of the article.

Ah, thank you, I wondered if that might be the case. "When usparkpolicepio says they didn’t use “CS or CN” tear gas, technically that’s correct. “OC” gas cannisters used instead. Causes same tears, tight breath and comes out green. " So they didn't use 'tear gas', they used something that causes tears...

Funny, WP:Tear gas does list OC. As a targeted person, I couldn't really care less whether the active ingredient that irritates my eyes and lungs -- and would e.g. pose a significant health risk to someone with asthma -- is man-made or biological...

@stannius Yes - maybe my grim, wry, extremely dry humour didn't come across in my comment. To be clear, I think they are playing semantics, and I don't think the people unnecessarily, disproportionately and possibly unlawfullly impacted by this give a stuff about the chemical formula, nor should they.

@MasonWheeler 1) there is no reliable source supporting the claims about people throwing things at the police 2) Even if we assume that a few people threw things- which the sources don't support -, deploying tear gas against peaceful protestors & violence against the media is hardly reasonable self-defense, but can best be described as an attack; using whitewashing terms like "crowd control" or "dispersal" on the other hand purposefully distort what happened, which imho isn't appropriate here

@MasonWheeler You're welcome to provide an answer that disproves the numerous bodies of evidence from multiple sources that the protesters were in no way aggressive. Until or unless you do, I'd suggest being careful of your glass house.

@tim "here is no reliable source supporting the claims about people throwing things at the police" What is your definition of "reliable source" that excludes the law enforcement and NPS police?

@Hasse1987 The many films and videos made by independent journalists and bystanders at the time - which don't support those claims.

@MasonWheeler Have you watched any of the videos of this protest? For example the attack on Australian journalists? I don't see any way to justify those actions.

@Araucaria-Nothereanymore. That means you have multiple contradictory reliable sources, a common situation, not that there are no reliable sources supporting "those claims".

@Hasse1987 If that were the case there would be footage showing the 'contradictory claims', and lots of it. There isn't.

@Hasse1987 reliability often comes from independence. The police are not an independent source in this case since they have a vested interest in their own actions not being perceived as overly severe. More independent sources such as some media outlets and passive standers-by would be considered reliable in this case.

Why did they order it? It looks like it was so they could shoot a video: twitter.com/i/status/1267676026391404544

@Araucaria-Nothereanymore. And how do you plan to go about establishing there isn't such footage?

There's some additional support for the (largely meaningless semantic) claim that "pepper balls" are "tear gas" besides the CDC: AP FACT CHECK: Trump denies tear gas use despite evidence. That cites a public health professional, the CDC, The Handbook of Toxicology of Chemical Warfare Agents, An Army research institute paper, and a tear gas researcher.

@Hasse1987 Because there is huge interest in making such footage public, both on the part of the police, of the government and of journalists. In those areas where there has been violence, however limited or not, on the part of demonstrators, for example against Fox News journalists, it has been well circulated and demonstrated. Same for those cases in other areas where again, however limited, there has been violence against the police.

@Araucaria-Nothereanymore. Yes some footage of violence has been circulated. And you have no idea what proportion of violence that footage represents, do you? Is this all based on assumptions about people's motives?

@Hasse1987 I am not aware of, or aware of any reports of, of any footage of any violence in Lafayette Square leading up to the tear-gassing of people demonstrating there before the area was cleared for Trump to have his photo. Call me a Skeptik, but can you provide the footage and any providence?

@Tim: You acknowledge that the motivation part is off-topic for skeptics.se. Unfortunately, it seems to be triggering other answers sharing more and more opinion-based idea of motivation. You okay with removing that part?

Huh, I said "other answers" because I thought there were three in total. My mistake.

@Oddthinking With "internal motivation" I mainly meant "was it done specifically because of a desire for a photo shoot" vs some other motivation (to show strength, because the curfew was going to start soon, 'just because', etc). I think whether or not it was in response to violence is a factual claim which can be answered and which provides some context to the question, so I think I'd prefer to keep it.

If the issue is mostly in preventing speculation in other answers, I think it might make sense to edit the question though (removing the "to [...]" part)?

@tim Totally support that notion. If cops/govt report it was because of some violence, it's very relevant to point out news media disagrees and there's no video or even witness evidence.