The arrest of four people on immigration-related charges Tuesday on Tucson’s south side sparked outrage on social media.

A video of the incident, which started with a traffic stop near the intersection of West 22nd Street and South Ninth Avenue, was posted on Facebook. It has had nearly 18,000 views since Tuesday afternoon. And 150 people have donated to an online fundraising campaign for family members taken into custody that has raised nearly $6,000.

On Wednesday afternoon, about 100 people gathered at nearby Southside Presbyterian Church, which has a long history of working for immigrant rights, to learn about the arrests and demand the release of the father, mother and 12-year-old daughter taken into Border Patrol custody during the stop.

The video shows a Border Patrol agent putting a man, woman and girl in the holding compartment of an agency vehicle. Moments later, a man lay down underneath the vehicle in an apparent effort to stop the agent from driving away. A passerby yelled at the man to get out from under the vehicle.

Border Patrol agents responded after a state trooper stopped a vehicle for a traffic violation and requested that agents investigate, according to a statement from the federal agency’s Tucson Sector.

A crowd gathered as agents arrested three people on immigration violations and one person on suspicion of impeding an investigation. The crowd was “dispersed peacefully.”

“The three individuals, a father, mother and their 12-year-old daughter, arrested for being illegally present in the United States remain together in Border Patrol custody as they are processed for immigration violations,” according to the statement.

The man who lay down under the vehicle was arrested and released, according to the Border Patrol.

The Arizona Department of Public Safety, which initiated the traffic stop, has not responded to inquiries from the Arizona Daily Star. Activists said the family was pulled over because the trooper believed the car’s window tint was too dark.

Jessica Rodriguez, the coordinator of the worker program at Southside, said Tuesday’s arrest was a rare case where activists witnessed a DPS trooper stop someone and call the Border Patrol.

Normally, state troopers stop drivers on highways where activists cannot intervene. This time, the arrest happened on a neighborhood street and activists’ “rapid response” network allowed them to arrive quickly, Rodriguez said.

Rodriguez and others at Wednesday’s news conference contested the Border Patrol’s statement that the family was kept together while in detention.

“We know they separated the girl from her mother last night. The girl slept alone in the hielera,” Rodriguez said in Spanish, using a slang term for Border Patrol detention centers where temperatures are kept low.

The Border Patrol did not release the names of those arrested, but a news release from local immigrant-rights activists said they were Glenda de la Vega Fernandez, Jesus Antonio Torres, and 12-year-old Dariana Torres de la Vega. The family has lived in Tucson for 11 years and have two other children, ages 10 and 6.

Alison Harrington, the pastor at nearby Southside Presbyterian Church, was leaving the church when she saw the arrests, she told the Arizona Daily Star. She described the scene as “heartbreaking” and “horrific.”

The 12-year-old girl was distraught and vomited during the arrest, Harrington said. Family and friends were nearby, but the Border Patrol agent would not release the girl to them.

The girl was still recovering from a respiratory illness when she was arrested, friends of the family told the crowd gathered at the church on Wednesday.

Harrington told the crowd, which included nine children whose parents were detained by immigration authorities in the past week, that as a community they would “demand the immediate reunification and release of Glenda, Jesus and Dariana.”

“Every day, we talk about the devastation caused to families and to our communities by the machinery of deportations,” Harrington said. “Sometimes it can become an abstract nightmare, and then every so often you witness it with your very own eyes.”

“You see the weeping mother telling her child ‘don’t cry’ as they are both led into a Border Patrol vehicle. You see the devastation of a father as he is handcuffed,” Harrington said.

“And you see the other members of the family begin to arrive on the scene with tears streaming down their faces,” she said. “You see the two little boys, the other children of Glenda and Jesus, running towards the Border Patrol vehicle crying, witness to their parents and big sister being taken away, left clinging to other family members, weeping, inconsolable.”

Tucson police and Pima County sheriff’s deputies were called to the scene of Tuesday’s arrest, according to the Border Patrol.

Tucson Police Department spokesman Officer Francisco Magos said in a statement, “We were requested to assist on a traffic stop that DPS initiated and asked for BP to respond. Our officers had no action in the situation.”