Chicago police said they were pursuing “good leads” Monday to find the gunman who shot and killed a man and wounded two other people in a pedestrian tunnel that connects the Red and Blue line Jackson stops.

The Loop shooting was at least the third attack on or near CTA train platforms in less than two weeks, and it caused trains to bypass the Jackson Red and Blue line stops during rush hour as the investigation spanned into the late morning.

The attack prompted officials to increase patrols on public transportation Monday morning, and a “comprehensive transit safety plan” will be announced in coming weeks, according to Chicago police spokesman Anthony Guglielmi. Last week,...