A disgusted Cornell University student ratted on his accused rapist frat bros by turning over a key piece of evidence — a SnapChat message proclaiming “free p–sy’’ in the form of the allegedly incapacitated student — to the victim, the accuser’s lawyer told The Post on Monday.

Lawyer Thomas Giuffra also revealed how Cornell Police and the local upstate district attorney allegedly failed his client in nailing her assailants — and how the school in Ithaca, New York, essentially forced the 20-year-old victim to remain enrolled on the same campus as her attackers by refusing to refund her tuition so she could study somewhere else.

Giuffra said the DA’s failure to perform any investigation two years ago, letting the campus cops go solo, means much evidence is lost except for one key piece — the sickening text advertising “free p–sy” among the frat brothers during the gang rape.

An anonymous “honorable” Chi Phi frat brother in the group chat later shared it with his client, Guiffra said.

“Had members of the fraternity been interviewed, and leads followed up, I believe we would have much more detail about what had occurred,” the lawyer said.

No one has been charged over the horrific accusations, but after the woman filed a civil suit in Manhattan court earlier this month, the Tompkins County DA announced he is reopening an investigation into the case, citing allegedly previously unknown details about what may have happened.

Giuffra said the university meanwhile only made matters worse for his client when it refused to refund her tuition after the alleged gang rape so she could leave the school and go somewhere else.

She doesn’t come from a wealthy family, meaning she was effectively forced to stay on campus for months while her mother came to take care of her, the lawyer said.

“Not a lot of humanity thrown around,” Giuffra said.

Cornell did not respond to a Post request for comment.

Giuffra ripped authorities over their handling of the case from the outset.

“Other than her initial contact with Cornell Police, she was not contacted by investigators from the Tompkins County District Attorney’s Office or any investigators trained in interviewing rape survivors,” Giuffra said of his client.

“It is challenging for me  to understand how a thorough criminal investigation could have been conducted when she never spoke with anyone other than the officer who took her original complaint,” Giuffra told The Post.

DA Matthew Van Houten said Monday that the victim’s original accounting of the night never claimed that she was “drugged against her will or gang-raped,” citing a six-page statement given to Cornell University Police by the woman at the time.

Shockingly graphic portions of that initial victim statement was suddenly published on the Tompkins County DA website Monday, a move Van Houten declared would “clear up the misperceptions of our decision.”

While Giuffra said he appreciates the DA reopening the investigation, he said it may be too late for a true investigation.

“The defensive posture I have gleaned from the DA’s statements leads me to believe that they recognize that there were failures, and they are trying to excuse them,” Giuffra said.

“While I do not care for the attempt to blame Ms. Doe for these failures, we appreciate and support any efforts to prosecute the parties responsible for the assaults and will fully cooperate with the District Attorney’s Office to hold these men accountable.” 

Guiffra said that much of the details between the initial interview and the lawsuit are similar — including the extensive mentioning of heavy ketamine use — and added that any discrepancies in detail and length are “because I took the time to meet with Ms. Doe multiple times and learn the specific facts of what had occurred.”