"They have been very uncompassionate with us. We don't know anything up to this point. We don't know who leads the investigation," Valentin Tachiquin, her father, said at a news conference Monday.
Activists say witnesses have told them that the plainclothes agent was walking toward the woman's car, while the vehicle was slowly in reverse.
Pedro Rios, director of the American Friends Service Committee's U.S-Mexico border program, said it was premature to jump to conclusions after the account that police offered Tuesday, noting that authorities said the investigation was in its early stages.