Federal prosecutors relied largely on surveillance video that showed the migrant collapsing in a confrontation with the agent, Luis Fonseca, at a Border Patrol station in Imperial Beach in July 2011, shortly after his arrest on suspicion of entering the country illegally.
"The way it was portrayed, the jury was expecting much worse," Stuart Adams, Fonseca's attorney, said outside the courthouse.
The swift acquittal on one count of deprivation of rights under color of law comes as U.S. border authorities are under growing scrutiny for its rules on use of force. The Department of Homeland Security ordered a review of its policies and practices late last year and the department's inspector general is conducting its own study.
Adams said jurors were likely persuaded by a doctor of emergency medicine whose testimony challenged that the migrant fell unconscious, suggesting instead that he was faking. Other witnesses supported the defense case that the agent acted as he was trained and that the migrant disobeyed orders, he said.
Prosecutors said in a pretrial court filing that Fonseca kneed the migrant, Adolfo Ceja, in the thigh and ordered him to the ground. They said the video shows Fonseca's hand on Ceja's throat even as the migrant has his hands on the wall. Ceja turns limp and collapses to the floor "with seizure-like movements."
Ceja appears to quickly regain consciousness, at which time Fonseca kicks him, according to prosecutors.
Five days later, Ceja attempted to enter the country at a San Diego border crossing on someone else's identification and reported the incident to an inspector, triggering the investigation, prosecutors said.
Fonseca, who has been on administrative leave, declined to speak with reporters after the verdict but his attorney said he was eager to return to his job.
Critics of the Border Patrol's record on use of force condemned the verdict.
"This sends the wrong message to Border Patrol and fuels a culture of impunity in the agency," said Andrea Guerrero, executive director of advocacy group Alliance San Diego. "As a matter of policy and practice, it should never be acceptable to strangle someone who poses no threat, then kick him while he is down and walk away as if no harm had been done."