Graphic video released of man attacking teen outside NH gym

ROCHESTER, N.H. — A young woman in New Hampshire survived a frightening and disturbing attack outside a gym, and police are hoping that by releasing video of the incident someone will recognize the suspect and call authorities.

"He was there my whole shift, eight hours just waiting and I don't know why, I have no idea why,” 18-year-old Erin McCarthy told Boston 25 News.

WATCH: Man violently attacks teen outside NH gym

McCarthy was leaving a Planet Fitness where she works on North Main Street in Rochester around 10 p.m. on June 12 when video shows the man attacking her from behind.

MORE: Suspect wanted after punching teen 39 times outside NH gym

Rochester police have only released the first 15 seconds of the attack on surveillance video, but they say the suspect punched McCarthy 39 times, kneed her and kicked her.

In the video, McCarthy and the suspect don't interact at all, and she says she doesn't remember ever interacting with him.

"It could be a random act or it could be known associates,” Rochester Police Lt. Jeremy Aucoin said.

It's too early in the investigation for police to know the motive, but Aucoin said the fact that the suspect was wearing sunglasses at night could be telling.

"He was trying to disguise himself to a point so that nobody could identify him if they were outside. Luckily enough for us there was video surveillance to be able to get it and hopefully with the help of the public we'll be able to identify this person," Aucoin said.

While the investigation unfolds, McCarthy is on the mend physically and emotionally.

She has been using humor as a coping mechanism as she processes the reality.

"I can joke about it I can laugh it off but at the end of the day I know how messed up it was," she said.

The suspect is described as a white male in his 20s. He was wearing a white t-shirt, shorts, white sneakers, a baseball hat and sunglasses at the time of the attack.

Police said they believe he fled in a light-colored Ford Fusion or similar vehicle.

The Rochester Police Department is asking anyone who may have information that could assist with this investigation to call Officer Frank Porfido at 603-330-7128.