HOPATCONG -- An investigation is underway into an alleged assault of a bunny- suited prankster blowing an air horn by a borough police officer after video of the incident surfaced online, authorities said.

Kevin Hemmerich, 28, of Hopatcong

Kevin Hemmerich went to the Hopatcong police headquarters on Thursday evening with the intention of turning himself in for an outstanding warrant, and to record an air horn prank at the same time, his brother, Jason, told NJ Advance Media Friday.

A video filmed by Jason Hemmerich and posted on Facebook Live and YouTube shows Kevin Hemmerich wearing a bunny costume and blowing an air horn over the course of four minutes despite being asked to stop.

After blowing the air horn intermittently, two officers then enter the lobby where the Hemmerich brothers were located. Jason Hemmerich said the duo began cursing and yelling and one of them punched his brother in the face. The other, he said, slapped the phone out of his hands.

"This is my hometown and he punched my brother in the face for no reason," he said.

Jason Hemmerich said his brother wasn't violent or a threat to police at the time he was hit. He also said he hasn't spoken to his brother since his arrest on Thursday night.

Jason Hemmerich said his brother had a warrant out for his arrest for failure to complete 12 days worth of work with the Sheriff's Labor Assistance Program. Kevin Hemmerich received the sentence in lieu of jail time for a failure to have auto insurance in connection with a motor vehicle crash.

Jason Hemmerich said he and his brother were admittedly playing a prank when his brother surrendered himself while wearing the bunny costume and blowing an air horn, but he believes borough police overstepped when they hit his brother, who wasn't posing a threat to officers, and slapped the phone out of his hand.

Jason Hemmerich said Hopatcong police had charged him with harassment and obstruction for filming the incident.

Sussex County First Assistant Prosecutor Greg Mueller said his office would be handling the investigation into the alleged assault and "the appropriateness of the charges against the brother." His office, he said, wouldn't be releasing the names of the officers involved at this time.

Mueller said later in the afternoon Friday the officer who slapped Kevin Hemmerich has been placed on administrative duty pending the outcome of the investigation and will not have interactions with the public.

Justin Zaremba may be reached at jzaremba@njadvancemedia.com. Follow him on Twitter @JustinZarembaNJ. Find NJ.com on Facebook.