D avid Koelsch, a former immigration judge based in Maryland, was in Minneapolis visiting his mother and sister the day Alex Pretti was shot and killed by federal agents. He drove to Nicollet Avenue, parked a few blocks away, and walked toward the scene. “I didn’t go there to protest. I didn’t bring a sign. I didn’t bring anything. I just went to stand and bear witness,” Koelsch said. What he saw shook him. Koelsch, 59, had never seen Immigration and Customs Enforcement (ICE) and Customs and Border Protection officers up close in full tactical gear, masked, armed with rifles and pistols, blocking off the street. About 50 to 75 agents stood in the road. Dozens of civilians watched from the sidewalk. People were yelling. Then the teargas came. “My chest started getting tight,” he said. “I felt like throwing up.” He dropped to his knees, then scrambled half a block away. After a few minutes, he could breathe again.…