Federal law enforcement officers have used unmarked vehicles to detain protesters in Portland. Videos shared online show officers driving up to people, detaining them without explanation, then driving off, Oregon Public Broadcasting first reported. The ACLU filed a lawsuit Friday evening to try and end what it called "lawlessness" on the streets of Portland. The lawsuit ... seeks to block the Department of Homeland Security and other agencies from attacking journalists and legal observers at protests. "Federal agents are terrorizing the community, threatening lives, and relentlessly attacking protesters demonstrating against police brutality," the ACLU said. "This is not law and order. This is lawlessness - and it must be stopped." Conner O'Shea, 30, a Portland resident who's been attending protests for almost two months, told USA Today that early Thursday morning, around 2 a.m. he and a friend had left protests downtown and were walking back to their car when they were suddenly pursued by men who they believed to be federal agents. O'Shea did not see any sort of identifying markers on the men - badges or numbers or words on their camouflage uniforms. O'Shea managed to get away. But his friend Mark Pettibone, 29, has told media he was arrested and booked by federal agents. Pettibone told the Washington Post that officers placed him in a holding cell in a federal courthouse, where he was read his Miranda rights. After Pettibone ... declined to answer questions, he was released.