They have stealth edited the article to hide their lies. Original version: https://web.archive.org/web/20200629131242/https://www.washingtonpost.com/nation/2020/06/29/st-louis-protest-gun-mayor/
The Washington Post says the protesters were peaceful, but from the videos it seems they broke into the property: https://twitter.com/walterjwinchell/status/1277645739921899521?s=21
Also, the crowd did not look peaceful, and this event didn’t happen in a vacuum in regards to all the other violent protests.
So the headline is false and misleading.