The line of S.U.V.s and vans streamed through an open gate, many unmarked, but two had U.S. Customs and Border Protection logos. It was the staff parking lot at the back of Ruben Salazar High School in Pico Rivera, a city in Southern California where more than 90 percent of residents are Latino.

The sight of federal agents alone was alarming on June 17, less than two weeks after the Trump administration sent the National Guard to the Los Angeles region to protect federal officials who had ramped up their raids targeting undocumented immigrants.

Then, the agents, some wearing fatigues, emerged from the vehicles. At least eight of them ducked behind storage containers on campus, some peering over their shoulders. In the shadows, one at a time, the men appeared to relieve themselves, based on footage captured by overhead security cameras.

Officials at the El Rancho Unified School District, which serves more than 7,000 students southeast of downtown Los Angeles, demanded an investigation into those federal officers. They said the agents were not allowed to be on school grounds, let alone use the blacktop and walls of storage containers as impromptu urinals.

The incident was the latest example of how Southern California residents and local leaders have kept close watch on the federal immigration officers who have stepped up raids targeting undocumented immigrants in the region. The episode at Salazar High School was one of the first times this year that a public agency has circulated its own video of federal agents and used the footage to call out their behavior.

The ongoing sweeps of street vendors, day laborers and other workers in the region have had a chilling effect on Latino communities in the Los Angeles area, prompting many people to stay home from work and cancel public gatherings. Activists and bystanders, in turn, have used their phones to film the raids and then have shared the footage broadly on social media.