Surveillance video captured the entire incident on June 15th.
Video shows 20-year-old Connor Castellani being surrounded by at least five officers after he was kicked out of the Tropicana Casino for being underage, his hands behind his back.
Castellani empties his pockets, and minutes later, he walks away.
Then the video shows Castellani crossing the street and yelling at the police.
Approximately two minutes later, four officer can be seen wrestling the 20-year-old to the ground.
For the next 45 seconds, video shows police kneeing Castellani and striking him with batons.
They then try to handcuff him.
"I was just basically rolling up in a ball," Castellani said. "I said I wasn't resisting. I told them that, and they continued to beat me."
The officers manage to get Castellani on his stomach, with one hand almost behind his back.
At that time, a K-9 officer pulls up, jumps out of the car and sets his dog on Castellani.
"When the dog actually chomped on the back of my neck, I was also receiving blows to the back of my head with a fist," he said.
Castellani was charged with resisting arrest, disorderly conduct and assault on an officer and a canine.
He needed more than 200 stitches to close up wounds and dog bites on his head and neck.
The department and prosecutor's office are investigating, but the Atlantic City Police Department is sticking by the officers.
Chief Ernest Jubilee says it's too early to pass judgment.
"All I can tell you there is an internal investigation, and when it's over I'll be able to speak about the results," he said. "At the conclusion of the investigation, then we'll move forward from there."
Court records show the K-9 officer involved in the incident had 15 prior complaints related to excessive force or assault, but he was exonerated in all those cases. That officer, Sterling Wheaton, still has five additional suits pending against him.
Former police officer and law enforcement expert Lou Palumbo saw the video and backed the officers.
"I have to say that the amount of force that I believe they used here was appropriate, yes," he said.
But John Shane, a professor at John Jay College of Criminal Justice, disagreed, saying that from his perspective, the use of the dog was an unnecessary and potentially deadly use of force.
"I don't know of any training that allows police officers to launch the dog onto somebody's neck, which is right where the dog went," he said.
The mayor of Atlantic City called the video "disturbing" and asked the state's attorney general to oversee that investigation.