Three people were injured when gunshots were fired at the first 4/20 marijuana celebration in Denver since Colorado legalized the drug last November. It was one of many such gatherings around the world, The Christian Science Monitor reports. None of the victims was seriously injured.

Thousands of people ran for cover when the shots were fired. The event had an increased police presence because of the recent bombings at the Boston Marathon, the article notes. Tens of thousands of people attended the event at Denver’s Civic Center. A second rally scheduled for Sunday was cancelled.

Denver police released a YouTube video that showed a possible suspect, according to The Denver Post. They asked the public for help in locating the man.