Caleb Daniel Hughes, 26, was formally charged with third-degree assault against an at-risk adult, according to Adams County district attorney spokeswoman Krista Flannigan.

Hughes was off duty at the time the confrontation happened on June 7.

The case involves a confrontation at a Thornton Costco at 16375 N. Washington St. The 60-year-old Costco employee had asked Hughes to turn off his engine while filling his vehicle with gas, according to sources familiar with the investigation. After asking the second time, the off-duty officer flashed his badge and said what he was doing was not against the law, the sources said.

"He picked him up by the shoulders and tossed him backwards," said eyewitness Michelle Bussee. "Picked him up, this time put him in the stone pillar that's right by the gas pump. That's when he scraped up his elbow."

The attendant was trying to reach the emergency gas shut off when he was assaulted, the sources told 7NEWS.

Hughes told Thornton police that the attendant "rushed" him and tried to reach into the vehicle to turn off the ignition, the sources said. That's when Hughes pushed the attendant away, he said.

"This guy didn't do anything to (Hughes)," said Bussee. "(The attendant) was extremely polite and there was no reason for that reaction."

The case was presented to the Weld County District Attorney's Office, which charged Hughes on June 13.

Hughes is on an unpaid leave of absence while the Weld County Sheriff's Office investigates the incident. Weld County was requested as an independent investigator by the Platteville police chief, according to the sources.

Hughes is due in court on July 11. Third-degree assault is a felony charge. He also faces two charges relating to a December accident on U.S. Highway 85 north of Brighton.

According to the Colorado State Patrol, Hughes was charged with careless driving and leaving the scene of an accident after he flashed emergency lights on his personal vehicle in order to get a woman to move from the passing lane of Highway 85 . When the woman moved to the right lane, her vehicle was struck. Hughes is accused of leaving the location of the accident in order to participate in a Santa parade.

Hughes was arraigned on May 27 and entered a not guilty plea.

Court records also indicate he pleaded guilty to a disorderly conduct charge in 2003. The case was dismissed after he successfully completed a court-ordered program.

When reached at home, Hughes declined comment to 7NEWS.