TYSONS, Va. —

Steven Bun says he’s still shaken by what he witnessed on Thursday. He was out shopping with his girlfriend at Tysons Corner when something caught his attention.

“All I heard was just screaming, ‘It’s just water! It's just water! Stop.'"

And that’s when he says he saw 19-year-old Lia Chen, of Annandale, being body slammed by an officer.

RELATED: 19-year-old, 2 others arrested at Tysons Corner mall

Alarmed, Bun says he confronted police shooting a video with his cellphone. 

“I was like, 'Bro, like, calm down. Why did you do that? She's like quarter your-- you know, quarter your size’

"He touched my girlfriend. I was like 'Hey don’t do that,’" he said.  

"'He said ‘Or what? Or what?’ And then next thing you know, they threw me against the wall."

Bun said officers broke his watch, hurt his hand, arrested him and confiscated his phone. Police deny seizing his phone. 

Fairfax County police claim Bun was interfering with their investigation—telling us the incident began after one of Chen’s friends—22-year-old Molly Helmer-- was caught shoplifting from a store.

Helmer was given a summons for a future court date and according to police, that’s when Chen dumped her drink all over the store’s floor before walking away. 

Here’s what police told WUSA9 in a statement:

“Chen was taken back into the store, but attempted to break free from the officer and continued to act disorderly. To gain control and prevent her from harming herself or others, she was taken to the ground by the arresting officer and finally handcuffed”

Chen was charged with disorderly conduct. Bun was also charged with disorderly conduct.

"They acted like she had a gun or something,” Bun said.

“When I saw that, I pictured-- I have a daughter of my own. I pictured that was my daughter or my sister, Bun said. 

Bun says he is working with a lawyer and plans to fight the charges.

Sign up for the Get Up DC newsletter: Your forecast. Your commute. Your news.