The ruling shocked many in Mexico, where the case already had become emblematic of the impunity often enjoyed by wealthy males.
The 17-year-old victim testified she was dragged into a car between two young men, one of whom fondled her breasts and one introduced his fingers into her vagina.
The judge granted the youth an injunction to dismiss the case because "an incidental touching or fondling will not be considered sexual acts, if proof is not presented that it was done to satisfy a sexual desire."
Judge Anuar Gonzalez Hemadi also ruled the fact the victim was able to move to the front seat of the car after pleading with her attackers to stop proved she was not "defenseless," as he claimed the law required.
The prosecutors' office in the Gulf coast Veracruz said it "roundly" disagreed with the ruling and would appeal it, because "it violates the rights of a sexual attack victim." Mexico's Federal Judiciary Council said that in serious cases such as this, the defendant would remain in jail while the appeal is decided.
The council, the country's court oversight agency, may also decide to investigate the judge's action in the case.
The alleged sexual assault occurred in Veracruz in January 2015. The then 17-year-old victim was standing outside a club with friends waiting for her ride when four men, all wealthy and in their 20s, allegedly forced her into a black Mercedes. Two allegedly assaulted her in the car and when they arrived at one of their homes, she allegedly was raped by a third.
No charges were brought against the men until the girl's father started a public campaign denouncing them. They became known derisively through social media as "Los Porkys," after the 1981 movie about misbehaving U.S. teens in the 1950s.
People outraged by the latest ruling posted photos of Judge Gonzalez Hemadi on social media sites, with the slogan "Judge Porky" and "Don't forget this face!"
The Network for Children's Rights in Mexico said the ruling was "absurd" and called on Veracruz state to investigate the judge.
"This ruling represents a serious step backward in the access to justice for girls and adolescent women who are victims of sexual violence, and set a precedent for impunity," the group said in a statement.
Social and traditional media played a key role in getting the defendants charged in the first place.
After authorities appeared to ignore the case for months, her father took the story to the press in 2015, along with a video of three of the men appearing to confess. The men have since denied wrongdoing.
Weeks of social media outrage over apparent impunity for the wealthy young men followed by daily reporting in Mexico's national television and print news outlets appeared to finally force the state to bring charges.
Many complained about the judicial logic of the new ruling.
"(The victim) was not defenseless, given that she had the possibility of changing places (in the car) and thus avoiding the contact with the suspect," the judge ruled, despite the fact the victim said she had been pushed, had her cellphone taken away and said the perpetrators only laughed when she pleaded with them to stop.
"There is no evidence of a look, a comment, an intent or a suggestion in the testimony that would prove an intention by the suspect to satisfy a carnal desire or excessive (sexual) appetite or eroticism," the judge wrote.
