Newport Beach police thought they may have found a man who exposed himself to a woman Wednesday night, but it turned out the culprit is still at large.

A woman was running along the Back Bay near Santiago Drive and Irvine Avenue around 8:45 p.m. when she saw a man at the end of the trail exposing himself, police spokeswoman Jennifer Manzella said.

The woman couldn't call police from the trail, so she drove to a friend's apartment and reported the incident about 20 minutes later, Manzella said. By the time police arrived, the man was gone.

Around 9:30 p.m., police detained a man on another trail about two miles away near Bayview Way and Bayview Place, Manzella said. Officers held the man until the woman arrived and told them he wasn't the flasher.

The department said it is investigating the detention after receiving a complaint alleging that officers mistreated the man. Manzella said the department looks into any complaint it receives.

Police described the man they are looking for as white, in his 20s, about 5 feet 8 inches tall with an athletic build and short, dark brown hair.