A teenage girl struck by a shackle-wielding New Orleans police officer told authorities last year that she was having nightmares about her violent treatment at the city’s juvenile detention center, according to an investigative file released this week.

The September run-in prompted the firing last month of Officer Terrance Saulny, a 25-year veteran of the New Orleans Police Department who was found to have used excessive force in restraining the bipolar 16-year-old at the Youth Study Center.

Surveillance footage of the incident, released Wednesday by the Office of Independent Police Monitor, raised fresh questions about why Saulny faced no criminal charges after investigators determined he struck the unruly inmate at least twice with a set of four-point restraints.

The girl was not seriously injured but received a bruise on her lower lip and a small cut to her chest, according to an investigation by the Police Department’s Public Integrity Bureau.

“She’s in the detention center, so of course she may have done something to be in there. But that doesn’t give you the right to bang her up the way (Saulny) did,” said Michael Hall, a New Orleans attorney representing the girl and her mother. “He was fighting like she was a man.”

Hall acknowledged that the video he viewed — the footage, he said, rendered the girl’s mother “speechless” — contained no audio of the profanity the teen was alleged to have used toward officers as she protested her incarceration and pleaded for her mother. But he said Saulny appeared to commit an unnecessary battery on the girl rather than de-escalate the situation.

“It didn’t have to go the way that it went,” Hall said. “I’m sure they teach (officers) conflict resolution in the academy.”

Saulny’s attorney, Ted Alpaugh, predicted last month that his client would be vindicated on appeal. “I think if anybody who knows what they’re looking at sees the (video), they wouldn’t think” he used excessive force, Alpaugh said.

Simone Levine, the city’s deputy independent police monitor, said her office decided to release the video as part of its commitment to providing transparency within the NOPD.

The City Attorney’s Office declined to release the video last month, citing several exemptions to the state’s public records law.

The encounter happened Sept. 23 at the city’s juvenile lockup in Gentilly. The 16-year-old had been booked with purse snatching and resisting an officer and, even on her way to the detention center, broke into what police described as a “tirade” in which she threatened officers and appeared capable of harming herself. Her fit continued as police processed her into the Youth Study Center, as she protested her incarceration and insisted she hadn’t done anything wrong.

“She was raising hell,” Officer Lawrence Hall recalled in an interview with PIB, “calling people bitches, whores and ‘motherfracas.’ ”

After being placed in a holding cell, the girl began banging on the door, kicking the wall and crying uncontrollably. A police report described her as flailing about and reaching “an elevated state of irrational behavior.” Officers said they became concerned she might kick the door open.

“I wasn’t even under the impression that it was a female, the way that she was acting and her appearance,” Officer Kira Godchaux told investigators. “I thought it was a little boy in there.”

Attempting to calm the girl down, Saulny entered the cell with shackles but was quickly rebuffed. The officer told the girl to turn around and place her knees on the bench to be restrained. When she refused, Saulny began using his hands to try to turn her around.

When she pulled away, the officer “pushed (the girl) away from him to create space” and “began grabbing her to get her to the floor,” according to a report by Saulny’s supervisor, Sgt. Hudson Cutno. The girl continued to “passively resist,” Cutno wrote, and a “pulling match” ensued. At one point, Saulny is seen drawing back his right hand and, while still holding the shackles, striking the girl on the shoulder.

“It should be noted because the shackles are connected by a long chain and Detective Saulny did not take precautions to drop the shackles or maintain control of them, (the girl) may have been struck twice from the second shackle hurling its way across her body,” Cutno wrote. “The incident happened so quickly that without the proper video equipment to slow the footage, it is unknown if the second shackle actually physically made contact.”

Godchaux then entered the cell to assist Saulny and, using a “hold technique,” helped him take the girl down, the report says. Investigators determined that Saulny also struck the girl again on the right side of her hip as she went down.

“He went to hitting me where his handcuffs is in my chest,” the girl later told PIB investigators. “I was crying because he had slammed me on the ground and he had hit me on my lip and my face and stuff on the bench.”

The girl’s mother told police that she had not been surprised by her daughter’s outburst, saying the girl had been refusing to take her medication. But she later accused Saulny of downplaying her daughter’s injuries and telling her in a phone call that the girl had cut her lip in a fall.

In terminating the officer, the Police Department said Saulny had used excessive force and also lied when he claimed he had not used profanity toward the girl. “There is no place in the department for officers who choose to mistreat members of the public and lie about their behavior,” Superintendent Michael Harrison said in a statement last month.

Tyler Gamble, a Police Department spokesman, said the investigation “determined there was not enough probable cause that a crime was committed” to prompt an arrest.

The investigative file shows an FBI agent assigned to the bureau’s Civil Rights Division participated in the probe, suggesting the U.S. Department of Justice also has decided not to pursue criminal charges.

Hall, the attorney representing the girl, said Wednesday that he hoped the District Attorney’s Office would take a “long, hard look” at the case before deciding not to prosecute the officer. While the report says the girl sustained only minor injuries, he said she’s had at least one surgery stemming from to the incident and may undergo a second.

Levine, the deputy independent police monitor, has said her office disagreed with the Public Integrity Bureau’s decision not to refer the case for potential criminal charges. In light of the case, her office recommended all police officers assigned to the Youth Study Center be required to wear body cameras and receive new training.

Follow Jim Mustian on Twitter, @JimMustian.