The teenage girl who was slammed to the ground by a McKinney police officer during a rowdy pool party in 2015 has filed a federal suit against the former cop, the city and the police department.

In a complaint filed last month, Dajerria Becton and her legal guardian, Shashona Becton, allege that former Cpl. Eric Casebolt violated the girl's constitutional rights by using excessive force and holding her without probable cause. The family also claims that the city and the police department are to blame for her injuries for not training officers adequately.

Dajerria is seeking $5 million in damages, court records show. She was 15 when she was filmed crying face down on the grass while Casebolt pinned her with his hands and knees. The video of the June 2015 incident spread widely and brought national attention to McKinney and Craig Ranch, the upscale neighborhood where it happened.

In a prepared statement, city officials disputed Dajerria's claims against McKinney and its police force.

"The City of McKinney denies the claims alleged against it and the McKinney Police Department, and as such, will vigorously defend the recently filed lawsuit," the statement reads. "McKinney prides itself in cultivating the highest standards of training and professionalism for our officers, and it strongly believes that its standards and training will withstand legal challenge."

Casebolt's attorney, Jim Jeffrey, declined to comment. Last year, a grand jury decided not to bring criminal charges against Casebolt.

McKinney stepped into a nationwide debate about police treatment of minorities when officers responded to a disturbance at a private pool in Craig Ranch in the summer of 2015. Neighbors complained that a party there had spun out of control and that teenagers were jumping a fence to get to the pool. Many of the teens were black.

In her complaint, Dajerria said she had been invited to the pool party by a resident and that she was leaving, as Casebolt had requested, when he began assaulting her.

She told a court that Casebolt approached her with his baton raised, grabbed her by the wrist and dragged her down, pulling her hair as he slammed her face into the grass. She described how Casebolt pinned her down with one knee on her back and one on her neck.

Casebolt repeatedly grabbed the back of Dajerria's head and forced her face down, remaining on top of her for several minutes, according to the complaint. Dajerria told the court that Casebolt handcuffed her even though she was following his commands.

"The entire time D.B. she could do nothing [but] cry out in pain and repeatedly beg for her 'Momma' as she endured the pain inflicted upon her by Defendant Casebolt's physical assault," the lawsuit reads.

McKinney Officer Eric Casebolt pinned down teenager Dajerria Becton on June 5, 2015, while responding to an unruly party at a private pool in the Craig Ranch neighborhood. (YouTube)

Dajerria and her guardian told the court that Casebolt's use of excessive force caused physical injuries, along with psychological distress that continues to this day.

The family alleged that Casebolt acted within policy and practice at the McKinney Police Department.

"There exists a practice of excessive force incidents that result from the training or lack thereof, received by MPD officers," the lawsuit reads. "Upon information and belief, MPD officers are trained by individuals with little or no experience working in the field."

The suit doesn't elaborate on these claims.

Kim T. Cole, Dajerria's attorney, said at a news conference Wednesday that the girl is bullied at school and online daily. The attorney said a young woman threatened Dajerria with physical harm Tuesday but that the girl was too scared of police to report it.

"We raise our children to think that good will always prevail and that people are good and if you're ever in trouble, call the police, they will help you," Cole said. "And in this instance, she received a very rude awakening."

Casebolt resigned four days after the pool party. At the time, Police Chief Greg Conley called the officer's behavior "indefensible."

"Our policies, our training and our practice do not support his actions," Conley said during a news conference in June 2015.

Casebolt's attorney at the time, Jane Bishkin, said the officer's emotions got the best of him during the pool party call because of two tragic encounters earlier in his shift. He had consoled a widow whose husband had shot himself and helped talk down a teen who threatened to jump off her parents' roof, Bishkin told reporters in 2015.

Dajerria is seeking damages for mental anguish, loss of quality of life and attorney's fees, plus interest. She also requests punitive damages, which are not compensation but a penalty for the defendant.

"There's absolutely no amount on the planet that will adequately compensate her for the effect that this has had on her," Cole said. "It has completely changed her demeanor; it has changed her personality. It's horrific."

The girl's attorney approached the city last June and offered to cooperate with an investigation and avoid a lawsuit if McKinney paid Dajerria $2.5 million. Cole claimed that Dajerria suffers from "social damage" because of the incident and would do better in a private school.

As part of the proposed agreement, Dajerria's family also requested that all McKinney police officers be trained in use of excessive force, racial sensitivity and handling of juveniles.

Those subjects are covered in basic police training, according to the Texas Commission on Law Enforcement.

The city didn't take the deal. Later that month, the grand jury chose not to indict Casebolt.

After the decision, McKinney leaders hosted a community forum to discuss policing with residents. Cole said the city should have done more to assure people that it would take steps to prevent other incidents like the one at the pool party.

One approach the city has taken to improve its image relies on its neighborhood police officer unit. A few months after the pool party, cops began foot and bike patrols in the city's east side to build relationships with black, Hispanic and white residents. Officials said the effort was not directly related to the confrontation at Craig Ranch, which is in the city's more affluent west side.

Updated at 6 p.m.: Revised to include comments from a news conference and a response from Eric Casebolt's attorney.