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DENVER (KDVR) — Police are on the hunt for a person suspected of being involved in a Downtown Denver shooting Wednesday afternoon.

An exchange of gunfire could be heard outside of a federal building at 20th and Champa Streets just before 1 p.m. People ducked for cover as they heard gunshots, according to a witness.

“It all happened so fast,” said pickup truck driver Joshua Moore. “My friend confronted the other guy. The other guy started shooting at us.”

The Denver Police Department said there was an altercation between someone inside a pickup truck and a pedestrian. Federal agents stopped the truck, police said. Investigators could be seen examining a gun outside the truck. Police say two people opened fire. No one was injured.

One person in the truck was taken into custody.

Moore, who was released after being detained, says he and a friend were picking up his friend’s girlfriend when she pointed out a guy who she says harassed her.

“My friend had confronted him about harassing her,” Moore said. “The guy pulled a gun out and started shooting at us. My friend had a gun as well … so he fired back.”

Moore said his friend is the person police arrested. Police were still searching for the pedestrian as of late Wednesday.