On August 4th, during a major gun rights demonstration in Portland, OR, a right-wing group with a stockpile of weapons was stationed on the rooftop of a garage, overlooking the rally. The individuals, whose arsenal included long guns, were affiliated with the far right group Patriot Prayer.
The Portland police discovered the armed group and took their weapons, but did not arrest them. They later gave the guns back to the group.
The officers withheld this information from everyone outside the police department, including the mayor. It was only on Monday, over two months later, that this news finally came out.
According to The Oregonian:
That shocking revelation came Monday as Portland officials scrambled to find a way to end the repeated violent clashes between dueling political factions downtown...
Asked why the public was not told of the incident sooner, Chief Danielle Outlaw said, "Hindsight is always perfect." Outlaw said the Police Bureau warns the public that protesters may be armed. Both right- and left-wing demonstrators have come to Portland protests armed, she said.