MIAMI BEACH, Fla. -

A 50-year-old man said he tried stopping what he thought was a robbery, but was instead beaten up by a police officer who never identified himself as one.

"I saw a guy grabbing at her purse," Andrew Mossberg said Wednesday. "At that point, I thought it was probably a robbery."

Mossberg said he had no idea the man he thought was robbing the woman was actually a police officer.

"He was not in a uniform. He did not have a badge or gun or anything visible," said Mossberg.

On June 26 in the 700 block of West Avenue, Mossberg said he and his 12-year-old son were walking their dog when he saw a Megan Adamescu struggling with a man on the sidewalk. He said it was Philippe Archer, an undercover Miami Beach police detective (pictured).

According to a police report, Archer was responding to a call about an intoxicated woman who wouldn't leave the lobby of a building.

"His arms were like this big. You know, they're bigger than my legs," said Mossberg. "I'm not stupid. I'm not going to go after someone who's twice my weight and has another foot on me almost."

According to the report, Mossberg charged Archer, then called police.

"After he kicked her legs out from under her, I screamed, 'I've called the police! They're on their way!' He rushes me, kicks me in the head," said Mossberg. "I'm on the ground -- I'm not resisting, I'm not doing anything -- he punches me a couple times and I pass out. Next thing I know, I've got handcuffs on and I'm being put in the back of a car."

Police charged Mossberg with battery on a law enforcement officer, resisting with violence, obstruction, and disorderly conduct.

"One of the greatest works of fiction since Hemmingway was around," said Edward O'Donnell, Mossberg's attorney.

O'Donnell said it didn't take much for the state attorney to clear Mossberg of the charges.

"He had to falsify something to cover up what he did," O'Donnell added.

The Miami Beach Police Department launched an internal affairs investigation into the incident. Mossberg said he wants the state attorney to investigate, too.

"He should immediately have his certification pulled and he needs to be in jail," he said.

Archer wrote in the police report that he identified himself as a police officer several times during the incident.